Just How Sensitive Is Earth's Climate to Atmospheric Carbon Dioxide?

Two new studies look far back in geologic time to determine how sensitive the global climate is to atmospheric CO2 levels

By David Biello


CLIMATE RECORD: The records preserved in stalagmites and ocean fossilsm, such as those harvested from mud cores drilled by the "Resolution" pictured here, suggest that CO2 levels in the atmosphere have an outsized effect on the Earth's climate.


Carbon dioxide levels climbing toward a doubling of the 280 parts per million (ppm) concentration found in the preindustrial atmosphere pose the question: What impact will this increased greenhouse gas load have on the climate? If relatively small changes in CO2 levels have big effects—meaning that we live in a more sensitive climate system—the planet could warm by as much as 6 degrees Celsius on average with attendant results such as changed weather patterns and sea-level rise. A less sensitive climate system would mean average warming of less than 2 degrees C and, therefore, fewer ramifications from global warming.

Human civilization is now running an experiment (and without a control) that will definitively determine the answer. Scientists, however, have also realized that history can be a guide: Two new papers published in Science this week examine the historical record preserved in a stalagmite and microscopic seashells, respectively, to offer some clues.

Earth scientist Aradhna Tripati of the University of California, Los Angeles's Department of Earth and Space Sciences and her colleagues extracted a record of past atmospheric concentrations of CO2 stretching back 20 million years from the shells of tiny creatures known as foraminifera buried in a column of ocean mud and rock. The microscopic animals build shells of calcium carbonate out of minerals in seawater—a process that is affected by the water's relative pH (acidity), which is, in turn controlled by the level of CO2 in the atmosphere. More CO2 in the atmosphere means a more acidic ocean.

"The two species we picked to analyze [Globigerinoides ruber and G. sacculifer] are both ones that are around today, and the living animals actually have photosynthetic algae as symbionts, which means that they live in the surface ocean, since the algae require sunlight to survive," Tripati explains. And that means the fossil record of their shells will reveal the relative acidity of the surface waters in the ratio of boron to calcium as well as the specific chemical signature of the boron itself. "When seawater is more acidic, less boron gets incorporated into the calcium carbonate shells," she adds.

The researchers first matched this fossil record secured by the Integrated Ocean Drilling Program Expedition in the western tropical Pacific to existing records from bubbles trapped in Antarctic ice cores that stretch back 800,000 years, which preserve a precise record of past atmospheric composition. Thus reassured of the technique's accuracy, they plunged back into deep geologic time.

"Modern-day levels of carbon dioxide were last reached about 15 million years ago," Tripati says, when sea levels were at least 25 meters higher and temperatures were at least 3 degrees C warmer on average. "During the middle Miocene, an [epoch] in Earth's history when carbon dioxide levels were sustained at values similar to what they are today [330 to 500 ppm], the planet was much warmer, sea level was higher, there was substantially less ice at the poles, and the distribution of rainfall was very different."

Further, "at no time in the last 20 million years have levels of carbon dioxide increased as rapidly as at present," Tripati adds; CO2 concentrations have climbed from 280 ppm to 387 ppm in the past 200 years. And "our work indicates that moderate changes in carbon dioxide levels of 100 to 200 parts per million were associated with major climate transitions and large changes in temperature"—indicative of a very sensitive climate.

A nearly 400,000-year record of Ice Age transitions preserved in a stalagmite in the Sanbao and Linzhu caves of Hubei Province in China would seem to offer evidence in support of the sensitive climate scenario. The stalagmites, composed of calcium carbonate leached from dripping water, preserve a record of monsoon rainfall in the region by their composition. Paleoclimatologist Hai Cheng of the University of Minnesota and his colleagues then compared this record with climatic transitions, such as the shift into and out of an Ice Age.

The rock record reveals that such rainfall changes occur at the same time as general alterations in the relative strength of sunlight hitting the planet thanks to periodic shifts in Earth's orbit, known as Milankovitch cycles. At the same time as the solar heat increases, according to the monsoon record published in Science, CO2 levels also begin to rise.

"Climate systems are well linked worldwide, such as sea-level, CO2, ice sheet[s], the Asian monsoon, regional temperature and precipitation," Cheng says. "So a change in one of them could trigger changes in others." And that might mean the climate is too sensitive to tolerate current levels of CO2 without changing the conditions that have allowed human civilization to flourish in the past 10,000 years.

Effect of Environment on the Cracks Behavior in TA6V Alloy

Abstract:
To get more information on the fatigue behavior of Ti-alloys, the growth of long cracks and of physically short bidimensional cracks has been studied on a TA6V alloy.

This article presents some results obtained on the influence of the crack wake on the propagation of fatigue cracks in specimens tested in ambient air and in high vacuum.

Few researches have been carried out on the influence of environment on the fatigue propagation of short cracks apart from those specific ally related to the so called corrosive environments. Previous studies on 7075 aluminum alloys and a construction steel have shown that the initial growth of short cracks occurs at a much lower stress intensity range (AK) in an active environment (ambient air or nitrogen containing traces of water vapor) than in vacuum. However, Gerdes have shown that there is no significant difference in the initial stress level in air and in vacuum for small surface cracks initiated in a Ti-8.6 Al alloy.

Moreover, crack closure is known to play a dominant role in influencing near threshold growth rates. Through the removal of material from the wake of long crack arrested at threshold, several authors have studied the location and the origin of crack closure. It has been concluded that the behavior of short and long bidimensional cracks can be rationalized in terms of the effective stress intensity factor range for Al alloys and steels.

To get more information on the fatigue behavior of Ti-alloys, the growth of long cracks and of physically short bidimensional cracks has been studied on a TA6V alloy. This article presents some results obtained on the influence of the crack wake on the propagation of fatigue cracks in specimens tested in ambient air and in high vacuum.

The material used for this investigation was a forged Ti-6AI-4V alloy (wt % 6.27 Al, 3.86 V, 0.12 Fe, 0.18 O2). After forging the alloy was heat treated at 955?C for 1 h 30 min. and water quenched, followed by 2 h at 700?C and air-cooling.

Fatigue crack propagation tests were carried out under ambient air and high vacuum (< 5.104 Pa) on CT specimens 5 or 12 mm thick and 24 mm wide, at a test frequency of 35 Hz and a load ratio R = 0.1. Crack advance was optically monitored and crack closure was detected by mean of the compliance technique with a back face strain gauge.

A long crack was first obtained at a/w ~0.5 using a load shedding procedure down to threshold or at constant ?K. Then the plastic wake of the crack was progressively removed by spark erosion to obtain a crack length about 0.1 mm. Then the bidimensional short through cracks were propagated at increasing ?K.

Near threshold propagation of long cracks

The relationship between the propagation rate da/dN and the nominal (?K) and the effective (?Keff) stress intensity factor ranges are plotted for tests performed in ambient air at R = 0.1 and 35 Hz on the Ti 6AI-4V alloy. Decreasing the specimen thickness from 12 to 5.5 mm lowers the nominal threshold range but does not affect the effective threshold range (?Keff)th. Consequently the thinner specimen corresponds to a lower Kop level.
























Figure 1. Crack opening stress intensity factor Kop versus the remaining crack length ?a at different steps of crack wake removing procedure

The 5.5 thick specimens were tested in air and in high vacuum. A strong detrimental influence of the ambient environment on the resistance to crack propagation at low rates can be observed. The effective data confirm that the ?Keff concept cannot account for the influence of environment.

Consequently, the crack growth mechanism in moist ambient air (about 50% R.H.) must be different from the intrinsic mechanism governing crack propagation in vacuum. Similar behaviors have previously been observed on Al-alloys and steels, for which materials an embrittling effect of water vapor adsorbed at the crack tip has been proposed. A similar mechanism could be suggested for Ti-alloys.

Crack closure location to analyze the location of crack closure, the crack wake was progressively removed and Kop measurements were performed at each step of this procedure.

The evolution of Kop versus the remaining crack length ?a is plotted for cracks pregrown at threshold ambient air on 5.5 mm and 12 mm thick specimens. The lowering of Kop at decreasing ?a is more pronounced on the thinner specimen. At ?a ~0.1 mm no closure was detected on the 5.5 mm thick specimen while a substantial remaining closure effect was measured with the thicker specimen. The length, along which the decrease in Kop was observed, i.e. where crack closure is localized, is about 1.5 mm for the thinner specimen thickness and 0.7 mm for the thicker one.

A complementary test on a 12 mm thick specimen was performed at a constant ?K of 7.5 MpaV/m corresponding to a constant growth rate about 3x10-9 m/cycle. Removing the crack wake did not affect Kop except when ?a is 0.1 mm.

The same measurements were made on cracks pregrown at threshold in vacuum. It was seen that, as in air, Kop is lower for the smaller thickness but it is independent of ?a. Similar observations have been made on a construction steel type E460.

As a consequence of these observations, it appears that the short crack effect (defined as the decrease in Kop with ?a) depends upon the embrittling effect of environment for cracks pregrown near threshold in air. However, for the crack pregrown at a constant rate of 3x10-9 m/cycle, Kop is, as in vacuum, independent of ?a, which suggests that this embrittling effect in air occurs only at ultra low rates. But an environmental influence is also observed at rates higher than 10-9 m/cycle. This suggests the existence of two distinct regimes in environmentally assisted crack growth. Similar behaviors have been observed on Al-alloys and steels.

Short crack propagation

The short cracks here obtained on 5.5 mm specimens were propagated at increasing ?K. In vacuum, there was no difference between long and short cracks, which was consistent with the independence of Kop upon ?a. Initially, the short crack grew for about 0.3 mm at ultra low rates (about 3 to 6x10-11 m/cycle) without any detectable closure. There after, there was an abrupt acceleration of the crack rate and crack closure was detected; and then progressively, a behavior similar to the one of a long crack was reached for a crack length about 1 mm.

The effective data confirm the existence of a typical near threshold mechanism without closure, which is different from the mechanism governing the propagation above 2x10-10 m/cycle. The microfractographic aspects of the fracture surfaces show that, compared to vacuum, the fades in air appear more brittle with crystallographic facets corresponding to a grains and lamellae. This crystallographic aspect is more developed at ultra low rates. On going experiments will hopefully give new information, which may permit a deeper analysis of these crack growth mechanisms.

The main conclusions of the present study on short cracks obtained artificially from long cracks in a TA6V alloy are:

The following conditions are required to obtain a short crack effect:

a pregrown long crack near threshold in air

removal of crack wake.

Under such condition a propagation regime typical of ultra low rates, without detectable closure, is observed for short cracks grown in ambient air.

No short crack effect is observed in other studied conditions, i.e.:

short cracks obtained from long crack pregrown in air at a constant rate of 3 x 10-9 m/cycle (AK = 7.5 MPa/m);

short cracks in vacuum.

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Fabrication of Titanium and Titanium Alloys

Abstract:
Titanium and its alloys can be readily hot worked at temperatures generally somewhat lower than those used for steels. Techniques for press and hammer forging of titanium are essentially the same as for low-alloy steels. Good handling methods and plant layout will reduce the number of reheats necessary, minimizing contamination during forging.

Hot Working

Titanium and its alloys can be readily hot worked at temperatures generally somewhat lower than those used for steels. To minimize surface contamination, titanium should be held at high temperatures for only a short time before forging. The rate of contamination, relatively low up to 700°C, increases rapidly with increase of temperature.

All forging furnace atmospheres contain free or combined oxygen, and some absorption of this element inevitably occurs. In addition to visible scaling, diffusion of oxygen results in hardening of a relatively shallow underlying layer. The effect of nitrogen is not usually significant at preheating temperatures. Subsequent operations such as machining will remove the hardened surface layer, and the final product will have hardness similar to forging stock.

Hydrogen, however, diffuses more rapidly than oxygen and may penetrate the full section of the work piece, which can have a serious effect on properties. Such material can only be recovered by prolonged vacuum annealing. Hydrogen is absorbed from both reducing and oxidizing gas- and oil-fired furnaces, but at a tolerably slow rate under strongly oxidizing conditions.

The order of preference of preheating atmospheres is therefore dried air (electric heating), undried air (electric heating), oxidizing oil- or gas-fired furnaces. Direct flame impingement must be avoided.

Forging. Techniques for press and hammer forging of titanium are essentially the same as for low-alloy steels. Good handling methods and plant layout will reduce the number of reheats necessary, minimizing contamination during forging. Because of the rapid cooling and the fairly narrow hot working range, the chilling effect of tools should be reduced to a minimum by keeping contact time as short as possible. Preheating the tools also helps. Repeated light blows, or attempts to continue forging at too low a temperature, may promote internal cracking and should be avoided. Moreover, a large number of reheats with only a small amount of deformation between heats is also detrimental, because it leads to a coarsening of the microstructure and consequently poor mechanical properties.

In drop forging, die contours should have larger radii and fillets than those used for steel; the lower thermal contraction of titanium requires a smaller shrinkage allowance. Trimming should be carried out hot; furnace, drop hammer and trimming press should be as close together as possible to minimize preheating and avoid wasting time and heat. A final stress-relief anneal is recommended.

Forming

Annealed and solution treated sheet can be pressed, stretch-formed, spun and dimpled, but maximum deformation depends upon the load being applied slowly. Good results are achieved with hydraulic presses, the rubber-pad method being useful for forming light-gauge parts. Drop hammer forming, with heated blanks, is widely used for sheet metal parts of complex contour. Punch presses, which should be slowed down to half or one-third their normal speed, can also be used.

Blanks may be prepared for forming by shearing, sawing, nibbling or blanking, using slow cutting speeds. Edge condition is important, and edge cracking may be minimized by keeping the guillotine blade sharp and close fitting or by heating metal before shearing. All burrs must be removed and, for more difficult forming operations, cut edges may need filing or polishing.

Simple shapes can be formed at room temperature, deformation being limited by the strength and springiness of the material. Solid lubricants such as soap, molybdenum disulphide or graphite are preferred to mineral oils and greases. ICI "Trilac" coating and polythene sheeting have been found to effect considerable improvement in difficult pressing operations.

For more complicated designs, the work piece and, where possible, the dies should be heated to facilitate forming. The use of heat in forming increases ductility, which is reflected in lower minimum bend radii and reduces both the load required to effect deformation and subsequent spring-back, thus ensuring greater accuracy.

Furthermore, at elevated temperatures, the spread between yield and ultimate strengths is increased, which also aids forming. The temperature to select for hot forming depends upon the alloy and the severity of the shape to be produced. Good results can be expected using temperatures of about 200-300oC for commercially pure titanium and IMI Titanium 230, and 550-650oC for IMI Titanium 317 and 318.

Heat Treatment

With heating in conventional furnaces there is always some surface contamination and a risk of hydrogen absorption. Vacuum treatment, though ideal, is rarely practicable, so it is customary to use ordinary electric furnaces; hydrogen pick-up is not usually excessive. Fuel-fired furnaces should be avoided if at all possible; titanium rapidly absorbs free or combined hydrogen from the surrounding atmosphere, and this can be serious, particularly with thin sections.

Superficial hardening by oxygen diffusion is almost inevitable at the higher annealing and preheating temperatures suggested for some titanium alloys. The hardening effect is insignificant at low annealing temperatures but above 600°C may lead to surface embrittlement. Both the oxide film and the underlying oxygen-rich layer should therefore be removed by one of the methods of surface treatment; this is particularly important for high-strength alloys.

Machining and Grinding

Titanium and its alloys can be machined successfully on conventional machine tools provided that certain requirements are satisfied. In all machining operations rigidity of both work piece and cutting tool is desirable. Best results will be obtained if the cutting tools have a good surface finish. If the cutting tools are in good condition, it is no more difficult to machine titanium than an alloy steel of equivalent strength.

Titanium has a tendency to gall or smear on to other metals. Sliding contact between the work piece and its support should be avoided, and the use of roller steadies and running centres is recommended.

Turning. In general, cutting speeds should be low and feeds as coarse as practicable. A good surface finish can be obtained with very coarse feeds by using suitably shaped tools with a large nose radius. This will, however, be limited by work piece rigidity as a large nose radius causes increased tool loads and work piece deflection. Due to the lower elastic modulus of titanium, these deflections are greater than would occur on steel workplaces.

Tool materials may be high-speed steel, cast alloy, or tungsten carbide. The "super" grades of high-speed steel are satisfactory, giving good results in turning where large feeds can be employed, and particularly where the surface is rough or the cut intermittent. Tungsten carbide may be necessary for heavy work on certain harder alloys or for intermittent cutting, but in general its use is confined to lighter, more continuous cuts. For economic use of carbide tools it is essential to regrind before wear becomes excessive, and mechanically clamped tips are an obvious advantage.

Threading. Single-point screw cutting is preferable to threading with a die. Conventional methods of screw-cutting can be used, but success can also be achieved when increments of cut of 0.25-0.50 mm are applied at right angles to the axis of the component. Cuts of less than 0.13 mm should be avoided. Machine tapping with cutting speeds up to 6 m/min is preferable to hand manipulation. Tapping of full threads should be avoided: a thread of 80% depth is much easier to tap and loses little strength.

Planing. Shaping and planing of titanium are not difficult, provided that the foregoing requirements of rigidity, speed and feed are satisfied. Tungsten carbide tools with a large radius, producing a broad and relatively thin chip, are most successful. As in all cutting operations, it is essential to use sharp tools and replace them before appreciable wear occurs. For planing, clamped circular buttons of tungsten carbide have obvious advantages.

Milling. In milling, the chief problem arises from chips welding on to the teeth, resulting in cutter chipping and breakage. This is minimized with climb milling, in which the tooth finishes its cutting stroke when moving parallel to the feed. Absolute rigidity is necessary to avoid chatter, but the chip is only attached to the tooth by a thin sliver which is easily broken off.

Drilling. Titanium may be drilled with short high-speed-steel drills; the holes should be as shallow as possible. A 140o point is best for sizes below 6-5 mm and a 90° or double-angle point for larger sizes. For holes of a depth greater than five diameters, it is helpful to retract the drill at intervals and clear the swarf. Flood lubrication with a heavily chlorinated cutting oil reduces frictional troubles.

Grinding. A reduction in wheel speed to a half or a third of the conventional speed, together with the use of a suitable coolant, will usually achieve an acceptable grinding ratio. Water-base soluble oils result in poor wheel life, but some chlorinated or sulphurised grinding oils, and solutions of vapour-phase rust inhibitors of the nitrite-amine type, are satisfactory.

Polishing. Titanium can be mechanically polished by techniques similar to those used for stainless steel; reductions in wheel or mop speeds are often beneficial. If a high polish is required, light pressures are necessary during the final operations. Good results have been obtained with a canvas wheel coated with 240E1 `Alundum` grit, which can be blended with stearic acid for a finer finish.

Descaling and Surface Treatment
When titanium and its alloys are heated in air, absorption of oxygen and, to a lesser extent, nitrogen, results in the formation of an outer layer of oxide and nitride and an underlying thin layer into which oxygen and nitrogen have diffused. Removal of this hardened metal layer is essential for optimum mechanical properties, and an integral part of any descaling process.

All types of scale can be removed in fused caustic soda, but use of an unmodified bath leads to hydrogen contamination and poor surface quality. The sodium hydride process results in good surfaces and efficient scale removal but, again, hydrogen contamination occurs. Consequently, neither process is suitable for thin sections.

Caustic soda with about 10% oxidizing additions can be used for slightly thicker material, descaling conditions being 20-30 minutes immersion (longer for very heavy scale) at 425°C. Reaction between titanium and any fused caustic soda bath may lead to a dangerous build-up of heat if a stack of thin sheet is descaled. Thin-gauge material should, therefore, be handled in small batches, at a temperature not exceeding 425°C.

Anti-galling Treatments. The tendency for titanium to gall when in sliding contact with itself or with other materials can be reduced by some form of surface treatment. This is particularly desirable for bearing surfaces and for threads of bolts. Both anodizing and `Sulfinuz` treatments reduce the galling tendency, while adherent nickel and chromium deposits provide good wear resistant surfaces. Cadmium plating or the use of anti-galling paints are effective in preventing seizure of bolt threads. Details of electro deposition and anodizing procedures are given in the following paragraphs.

Electrodeposition. Adherent metallic coatings can only be electrodeposited on to titanium if the surface is suitably prepared. A procedure which has been found successful for depositing nickel, chromium, zinc and cadmium on to some titanium alloys uses a pretreatment comprising: (1) Vapour degrease, (2) Hydrochloric acid etch, 5 min in concentrated HCl at 90-110°C, (3) Cold water rinse, (4) Nickel strike for 3 min, (5) Cold water rinse.

Anodizing. Surface properties of titanium and its alloys can be modified by anodic oxidation treatment, which covers the entire surface with a thin but compact oxide film. Almost any aqueous solution can be used, but immersion in a solution of 80% phosphoric acid, 10% sulphuric acid and 10% water gives a particularly coherent film. A potential increasing from 0 to 110 volts over ten minutes should be applied.

Anodized titanium has no affinity for dyestuffs, but the film itself shows interference colors, determined by the final anodizing potential.

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Titanium and Its Alloys

Selection of Materials and Applications
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Abstract:
In selecting titanium and its alloys for any particular application, the engineer must consider both the economic and technological justification for the utilization of this metal in specific components.

Even at the current premium price of titanium, many items for civilian and military uses are justifiable in titanium. In many items the initial high cost of the material is compensated for either by the advantages of weight reduction due to the low density of the metal or by the increased life of the component due to high corrosion resistance of the metal.

The importance of titanium, or any other material for that matter, can be no greater than the use to which it is put. In selecting titanium and its alloys for any particular application, the engineer must consider both the economic and technological justification for the utilization of this metal in specific components.

Even at the current premium price of titanium, many items for civilian and military uses are justifiable in titanium. In many items the initial high cost of the material is compensated for either by the advantages of weight reduction due to the low density of the metal or by the increased life of the component due to high corrosion resistance of the metal.

Since it is generally anticipated that the price of this metal will no doubt decrease with increasing production and improvement in processing, it is not intended here to treat fully, by any means, the economic considerations. Rather, it is intended to consider the technological justification required in utilization of titanium for the various components desired.

Two basic considerations must be appreciated: one stemming from the specifications of the component and the other from design. Specifications usually require the meeting of certain mechanical properties desirable in the end item. Such properties may include one or several of the following: yield strength, tensile strength, elongation, reduction in area, bend ductility, impact strength, hardness, fatigue strength, creep, and elevated temperature properties.

Upon selection of a material by the materials engineer which meets the basic minimum requirements specified, it then becomes the product engineer’s responsibility to consider the fabrication problems which are peculiar to the design. Here the capabilities of the materials to undergo the required fabrication methods to produce the desired end-product must be evaluated.

Selection of Materials

Good purity unalloyed titanium is cast, formed, joined, and machined with relative ease as compared with the alloy grades. In view of this, wherever the properties desired in the end item can be satisfied by the employment of unalloyed titanium grades, the selection should be made on this basis.

There is considerable variation in the properties offered by the unalloyed grades of commercial producers. Even with the same producer, variation has been noticed among heats of the same grade. As melting techniques are continually improved, greater homogeneity can be expected. Significant improvement has been made in this direction in the last few decades.

To insure the ease of fabricability, consistent with that of unalloyed titanium, the materials engineer should acquaint himself with the contaminating interstitial content of the metal in order that the material used will not exceed the maximum tolerable limits of these elements.

Where higher strengths are required or where special applications necessitate specific alloying elements, an alloy grade of titanium must be considered. Increasing the alloy content will increase, to a point, the strength, usually with an accompanying loss of ductility. This lowering of ductility indicates a lessening in the ease of formability.

In selecting an alloy, therefore, it is generally desirable to choose that alloy which offers the maximum formability for the strength level desired whether the strength requirement be tensile, fatigue, or creep strength. Where high strength and hardness are prime requirements, it may be desirable to select an alloy which exhibits a good response to heat-treatment. In this way the material can be heat-treated to obtain maximum ductility, rendering ease of formability. Subsequently, formed products can be heat-treated to the required strength or hardness.

Manganese and chromium binaries have generally not been found desirable as casting materials. Aluminum additions to these binary alloys improve the quality of the casting produced. Multicomponent alloys containing aluminum as the major addition have been found to offer better elevated temperature properties. It appears now that aluminum ternary alloys with either manganese, chromium, or vanadium will become the most useful titanium materials.

As a general guideline, employ unalloyed titanium wherever possible. Where alloy grades are required, the material which offers the best formability at the required strength level should be selected. Where possible, heat-treatment should be employed either to obtain the best ductility for ease of forming or to obtain maximum strength in the end product.

For adequate commercial utilization of titanium, it is necessary that the particular component be justifiable both from the standpoint of economics and technology. Designers and engineers have already found wide utilization for this lightweight, high strength, corrosion resistant metal encompassing many diversified applications.

Aircraft Applications

Aeronautical design engineers find in titanium and its alloys a metal whose light weight and high strength, particularly at elevated temperatures, render it a highly desirable material in aircraft construction.

Titanium is finding increasingly greater preference over aluminum and stainless steel in aircraft utilization. Aluminum loses its strength rapidly at elevated temperatures. Titanium, on the other hand, has a distinct high temperature strength advantage at temperatures up to 800°F (426°C); such elevated temperatures occur at high speeds due to aerodynamic heating.

The advantage of titanium substitution for steel in aircraft stems from its accompanying weight reduction with no loss in strength. The overall reduction of weight and the increased elevated temperature performance allowed by the utilization of titanium permit increased pay loads, as well as an increase in range and maneuverability. In view of this, effort is being applied to utilize this metal in aircraft construction from engines and airframes to skins and fasteners.

In jet engines titanium is chiefly used in compressor blades, turbine disks, and many other forged parts. The materials replaced in these applications are stainless and heat-treated alloy steels.

Marine Applications

The corrosion resistance of titanium and its alloys makes this metal a prime consideration for use in marine environments. The Navy is thoroughly investigating titanium’s corrosion resistance to stack gases, steam, and oil as well as sea water. Of almost equal importance in these applications is the high strength-weight ratio.

The light weight of the metal, in conjunction with the corrosion resistance, offers in naval vessels improved maneuverability, increased range, less preventative maintenance, and reduced power cost.

Naval investigations cover applications such as wet exhaust mufflers for submarine diesel engines, meter disks, and thin wall condenser and heat exchanger tubes. In the case of the exhaust mufflers, titanium may offer greater service life than is offered by most materials. Titanium as applied to meter disks should offer improved service in salt water, gasoline, or oil where present materials are inferior in one or more of these environments.

Also being investigated for possible utilization are heat exchanger tubes which must be resistant to corrosion by sea water on the outer walls and at the same time give equal resistance to exhaust condensate on the inner walls. Items such as antennas and exposed radar components, which require resistance to stack gases as well as to marine atmospheres, are also being considered.

Ordnance

Perhaps the largest potential military consumer of titanium products will be the Army Ordnance Corps. Much of the sponsorship of the early research and development on titanium stemmed from Army Ordnance. Many prototype components are currently being investigated by ordnance engineers. However, few production applications of the metal are standardized. The vast amount of development work and the few production items are indicative of the great interest shown by Ordnance and the limits imposed on production items by high cost.

Early investigation of titanium and its alloys indicated that the metal had promising armor plate applications. Tests on early titanium armor permitted a 25% weight saving by substitution of titanium for steel armor with equal resistance to ballistic attack. This was accomplished by replacing 1/2-inch armor plate with 5/8-inch titanium armor. With improved alloys an inch-for-inch substitution does not seem unreasonable. This would allow up to a 44% weight saving.

Employment of titanium on a production basis would allow greater maneuverability, wider traveling range, and greater useful life. For airborne transportation, the advantage of lightweight vehicles fabricated from titanium is obvious. The first standard application of titanium by Ordnance has been in the manufacture of a titanium alloy gas piston for use in some automatic weapons.

Transportation

Many of the advantages indicated for armored vehicles also apply to the transportation industry.

Decreased fuel consumption or increased pay load and better fatigue strength in piston rods and transmissions are possible advantages offered by the substitution of titanium for materials used in transportation industries today. In railway equipment applications, dead weight considerations are of utmost importance. Where the overall weight of a railway car can be substantially decreased by the application of titanium, it follows that the horsepower required to pull this lighter car will be markedly reduced, as will be the size required for the journals and the journal boxes.

Another application where load is a major consideration is in trailer trucks. Here, also, increased pay load can be achieved by the replacement of steel with titanium in such items as axles and wheels.

Chemical

In the chemical industry the corrosion resistance of a metal plays the most important part. However, light weight and strength are desirable. The advantages described there indicate utilization in many industries once the price is reduced to a competitive level.

Production equipment which facilitates transportation of corrosive materials such as acid, alkali, and inorganic salts are logical applications for titanium. Manufacturing equipment such as vats, reflux towers, filters, and pressure vessels give additional opportunities for the utilization of titanium.

Titanium tubing can improve the performance of heating coils in laboratory autoclaves and heat exchangers.

Miscellaneous Applications

The food, petroleum and electrical industries, as well as the field of surgical instruments and surgery itself, are representative of the diverse fields in which application of titanium has been found desirable.

Food processing tables as well as steam tables, where titanium has been substitute for stainless steel, have been evaluated and results indicate superior performance and potential utilization.

In oil and gas drilling applications, the corrosion problem is serious, and titanium substitution will permit less frequent replacement of corroding underground shafts. In catalytic processing applications and fuel pipe lines, titanium’s high temperature properties and corrosion resistance are desirable. Increased utilization is again dependent upon increased supply of the metal at reduced prices.

The electrical industry is equally desirous of taking advantage of the metal’s high strength-lightweight ratio and, in addition, its high electrical resistance and nonmagnetic properties for utilization as cable armor material.

Most industries employ fasteners in some form or other, and the production of titanium fasteners on a commercial basis has not been lacking over the conventional surgical instruments.

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