Tensile properties of chromium alloyed with silver

Tensile behaviors of chromium (Cr) and Cr alloyed with various contents of silver (Ag) have been studied in air at room temperature. The results show that adding Ag to Cr can greatly improve the latter’s tensile ductility: Cr-2 at. pct Ag alloy was subjected to about 23 pct tensile elongation at room temperature.     

Structure and properties of a microduplex maraging steel

A simple two-step thermal processing technique was devised to impart a microduplex structure in a high strength 250 grade commercial maraging steel. A martensite grain size of approximately 1 μm was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below theM _d temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The micro-duplex structure exhibited a slight improvement in fracture toughness at high strain rate in contrast to the martensitic structure in which the rate effect significantly reduced the toughness.     

Structure and properties of a microduplex maraging steel

A simple two-step thermal processing technique was devised to impart a microduplex structure in a high strength 250 grade commercial maraging steel. A martensite grain size of approximately 1μm was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below theM _d temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The microduplex structure exhibited a slight improvement in fracture toughness at high strain rate in contrast to the martensitic structure in which the rate effect significantly reduced the toughness.     

Superplasticity and residual tensile properties of a microduplex copper-nickel-zinc alloy

Structural superplasticity in two phase alloys of the copper-nickel-zinc system (nominal composition in wt. pct Cu-15Ni-38 Zn-0.2 Mn) occurs over a wide range of strain rates in the temperature range 850 to 1050∮F (454 to 565°). The upper temperature limit for super-plastic behavior in this system is determined by the reversion of the fine-grained two-phase structure to a single phase structure in which extensive grain growth is possible. Residual room temperature tensile properties and microstructure of the microduplex alloy after superplastic straining have been studied as a function of test temperature and total super-plastic strain. At test temperatures sufficiently removed from the phase transformation temperature, the high tensile properties and fine microstructure of the starting material are essentially retained after superplastic strains approaching 200 pct. In the immediate vicinity of the phase transformation temperature, rapid degradation of the microduplex structure occurs during superplastic deformation with a consequent severe degradation of the residual room temperature tensile properties. Formerly with The International Nickel Company, is now with Gulf Energy and Environmental Systems, Materials Science Department, P. O. Box 608, San Diego, Calif. 92112.     

Tensile properties of directionally solidified Al-4 wt pct Cu alloys with columnar and equiaxed grains

The tensile properties of directionally solidified Al-4 wt pct Cu-0.15-0.2 wt pct Ti alloys with equiaxed grains were determined and compared with the properties of directionally solidified Al-4 wt pct Cu columnar structures. The tensile properties of the equiaxed structure were isotropic, but varied with the distance from the chill face. The mechanical properties of the equiaxed structure were generally between those of the longitudinal and transverse columnar structures. The 0.2 pct offset yield stress(σ _y, MPa) is represented as a function of the grain size,d (mm), the average concentration, C_o (wt pct), and the local concentration, C (wt pct), by σ_y = [(15.7 + 22.6 C_o) + (1.24 + 1.04 C_o)d ^-1/2] + [15.7 △C], where △C = C - C_o. The equiaxed structure exhibits inverse segregation similar to that in the columnar structure.     

Microstructure and properties of spray-deposited 2014+15 vol pct SiC particulate-reinforced metal matrix composite

A metal matrix composite (MMC) of 2014 aluminum alloy reinforced with 15 vol pct SiC particulate was produced by the spray-forming-deposition process. The as-deposited preform revealed a high density and a homogeneous reinforcement distribution. Reactive products were not found on interfaces between the reinforcement and the matrix. Compared to the control alloy, the composite showed accelerated aging after solutionizing at 502 °C, while aging was retarded after solutionizing at 475 °C. Analysis indicated that the activation energy was almost the same for the aging process after different solutionizing treatments. This suggested that while the thermal barrier for the aging process was the same, other factors affecting the aging process should be considered. For example, the effective concentration of the precipitate forming elements possibly decreased after incompletely solutionizing at 475 °C. After heat treatment, the composite showed a tensile strength similar to the control alloy. The wear resistance of the composite improved considerably. The aging behavior of the composite was also studied using the nanoindentation technique. Steep gradient distribution of elastic modulus and hardness around the reinforcement SiC particulate was observed. Theoretical analysis showed that this could be attributed to the gradient distribution of precipitates, resulting from a gradient distribution of dislocation density around the SiC particulates caused by residual thermal misfit stresses.     

Microstructure transformation from lamellar to equiaxed microduplex through equal-channel angular pressing in an Al-33 pct Cu eutectic alloy

Strain-driven transformation of a lamellar structure into a homogeneous equiaxed microduplex structure was investigated in an eutectic Al-33 pct Cu alloy deformed by equal-channel angular pressing at 400 °C via route Bc. In route Bc, the rotation of sample is always 90 deg in the same sense, i.e., clockwise or counterclockwise. The transformation follows the subdivision of the colonies into smaller lamellar blocks, the separation of these lamellar blocks into isolated islands, and, finally, the shrinkage of these islands to disappear, through the breaking down of the lamellae near the boundaries of the lamellar block-and-equiaxed region. The kinetics of the strain-driven microstructure transformation process, described by the dependence of the relative lamellar area fraction on equivalent true strain accumulated by equal-channel angular pressing (ECAP), physiognomically resembles that of the thermally activated transformation process described by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the recrystallization process.     

Effects of Widmanstätten ferrite on the mechanical properties of a 0.2 pct C-0.7 pct Mn steel

Laboratory melted and rolled C-Mn steel plates were austenitized at either 925 °C or 1150 °C to produce nominal austenite grain sizes of 60 and 200 μm, resspectively. The plates were then cooled at rates in the range of about 2 °C/min to 400 °C/min to produce mixed polygonal ferrite/Widmanst?tten ferrite/pearlite microstructures. The percentage of Widmanst?tten structure (a Widmanst?tten ferrite/pearlite aggregate) increases with increasing prior austenite grain size and cooling rate. Both yield strength and impact toughness increase with decreasing austenite grain size and increasing cooling rate. This simultaneous improvement in strength and toughness is attributed to overall refinement of both the polygonal ferrite and Widmanst?tten structure. Both yield and tensile strength increase with an increase in the volume fraction of Widmanst?tten ferrite and a reduction in ferrite grain size. In contrast, the toughness level achieved in these polygonal ferrite/Widmanst?tten ferrite/pearlite microstructures depends largely on the ferrite grain size; the finer the grain size, the better the toughness.     

Tensile flow and fracture behavior of DO3 Fe-25 at. pct Al and Fe-31 at. pct al alloys

The tensile properties, fracture modes, and deformation mechanisms of two DO₃ alloys, Fe-25 and Fe-31 at. pct Al, have been investigated as a function of temperature up to 600°C. The first alloy was produced by powder metallurgy and hot-extrusion, the second by casting and hot-extrusion. At room temperature extensive plastic deformation occurs in these intermetallics, exhibiting an elongation to fracture of 8 pct and 5.6 pct, respectively. In the Fe-25Al alloy the deformation process consisted of motion and extensive cross-slip of ordinary dislocations and associated formation of antiphase-boundary (APB) bands, while in the Fe-31 Al alloy, plasticity occurred by the motion of superlattice dislocations which eventually dissociated to form APB bands. At room temperature both alloys exhibited transgranular cleavage fracture modes. The variation of tensile properties and fracture modes with temperature is presented. H. A. LIPSITT, formerly with the Materials Laboratory of the Air Force Wright Aeronautical Laboratories, Wright-Patterson Air Force Base, OH 45433-6533     

Rheological behavior of Sn-15 pct Pb in the crystallization range

Rheological behavior of Sn-15 pct Pb alloy in the solidification range has been investigated using a Couette type viscometer. In samples partially solidified before shearing, deformation is localized and primarily intergranular. Samples containing more than about 0.15 fraction solid exhibit an “apparent yield point” which is on the order of 10⁶ dyne per sq cm and increases with increasing fraction solid. When shearing is conducted continuously while the alloy is cooled from above the liquidus to the desired final fraction solid, shear stresses required for flow are reduced by about three orders of magnitude. The solid-liquid mixture now behaves as a fluid slurry. Structural examination shows that shear takes place throughout the cross section of the specimen and that the solid is present as a fine grained particulate suspension. Flow behavior can be described by a viscosity which depends on fraction solid, decreases with increasing shear rate and exhibits hysteresis when shear rate is changed. For shear rates of 200 sec⁻¹, at 0.40 fraction solid, viscosity is about 5 poise which is equivalent to that of heavy machine oil at room temperature. The fact that the slurry is highly fluid at large fractions solid suggests potential applications in new and existing metal casting processes. Formerly Research Assistant, Department of Metallurgy and Materials Science, M.I.T., Cambridge, Mass.     

Response of semi-solid Sn-15 pct Pb to rapid shear-rate changes

Semisolid metal alloys, used in thixoforming, are thixotropic. The slurry viscosity is shear-rate- and time dependent provided the microstructure in the semisolid state is nondendritic and consists of solid spheroids surrounded by liquid. Thixoforming takes less than 1 second, during which time the structure of the material breaks down. This breakdown can be studied by viscometry, using rapid data-collection rates, by imposing rapid increases in shear rate on the slurry. An initial rapid (<1 second) structural breakdown during a shear-rate jump is followed by a more gradual decrease in viscosity, lasting several minutes. The slurry breaks down more rapidly with a higher final shear rate, but the first breakdown time is independent of the initial shear rate. The reverse is found with the shear-rate drops: recovery times increase with increasing final shear rate. Again, this time is independent of the starting shear rate. The shear stress and viscosity during initial breakdown and initial recovery can be described by single exponential equations. Build-up processes were examined by performing jumps after allowing the slurry to rest at a zero shear rate for different times. The increase in peak stress with rest time reflects the evolving degree of particle agglomeration. Microstructural examination confirms this phenomenon.     

The tensile properties of an Fe-4 pct Mo-0.2 pct C martensite tempered under applied stress

In Fe-4 pct Mo-0.2 pct C martensite which is a typical secondary hardening steel, premature failure o°Curred in tensile test at 600 °C to 700°C where solute atoms could diffuse easily. To clarify this phenomenon, the quenched specimens were tempered under applied stress and tensile-tested at room temperature. The following results were obtained: (1) Typical intergranular fracture was observed in specimens tempered in a temperature range of 600 °C to 650 °C with tempering times of five minutes to 10 minutes and applied stress (70 MPa to 140 MPa). (2) Based on Auger analysis, this phenomenon was considered to be caused by segregation of P, S, and Mo on prior austenite grain boundaries due to applied stress. (3) The direction of applied stress was found to be very significant. Namely, when the tensile direction was parallel to the applied stress during tempering, the specimen was more brittle, and when tensile direction was normal to the applied stress, the specimen was not so brittle. (4) To reduce this embrittlement, solution treatment temperature was adjusted, and it was found that the embrittlement was considerably reduced both in specimens with fine prior austenite grains and with some ferrite phase on prior austenite grain boundaries. TAKATOSHI OGAWA, formerly with Kyoto University. YOSHIFUMI OHMURA, formerly with Kyoto University. This paper is based on a presentation made at the “pcter G. Winchell Symposium on Tempering of Steel” held at the Louisville Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy and Heat Treatment Committees.     

Tensile properties of a thermomechanically processed ductile iron

A ductile cast iron was continuously hot-and-warm-rolled or one-step-forged from a temperature in the austenite range (900 °C to 1100 °C) to a temperature below the A ₁ temperature. Various amounts of reduction were used (from 60 to more than 90 pct). Tensile properties including tensile strength and total elongation were measured along the directions parallel and transverse to the rolling direction and along the direction transverse to the forging direction. The tensile ductility and strength both increase with a decrease in the amount of hot-and-warm working (HWW). Compared with the results obtained by other investigators, the present results showed higher strengths and ductilities over the same range of reduction in thickness. The improvement in properties is related to the lower temperature of the postprocessing heat treatment given in this study (600 °C) compared to other studies (900 °C). The low temperature of heat treatment leads to a structure of fine graphite in a matrix of ferrite and carbides, whereas the high temperature of heat treatment leads to coarse graphite in a matrix of carbide-free ferrite. The delay in failure from the presence of the small graphite constituent results in an increase in tensile ductility with an accompanying increase in tensile strength.     

The effect of alloying additions on the superplastic properties of Ti-6 pct Al-4 pct V

The superplastic deformation properties of Ti-6 pct Al-4 pct V and modified alloys containing 1/4 pct, 1/2 pct, 1 pct, and 2 pct of either cobalt or nickel have been investigated in the temperature range 950 to 750 °C. The results show that both cobalt and nickel modified alloys have reduced flow stresses, in comparison with Ti-6 pct Al-4 pct V, the reductions being particularly marked at the lower temperatures and lower strain rates. The results are shown to be consistent with an isostress model for the deformation of (α + β) two-phase alloys in which the varying β volume fractions and differing diffusivities of titanium, cobalt, or nickel in the β phase are taken into account.     

Effect of phosphorus on the mechanical properties of normalized 0.1 pct C, 1.0 pct Mn steels

The effect of phosphorus, in amounts up to 0.2 pct, on the stress-strain characteristics and strain-rate sensitivity of a series of laboratory-produced 0.1C–1.0Mn steels has been determined on normalized 10 mm-thick (0.38 in.) plate at temperatures from −196 to 400°C (−321 to 752°F). It was found that 0.05 pct phosphorus increased the yield strength of the 0.1C–1.0Mn steel about 24 MPa (3.5 ksi) at 22°C (72°F) and above without significantly affecting the Charpy V-notch shelf energy or fracture-appearance transition temperature. Additions of 0.1 and 0.2 pct phosphorus caused a greater increase in the yield strength (48 and 93 MPa or 7 and 13.5 ksi) but also increased the transition temperature. The strengthening effect of phosphorus in these steels is much the same as that found previously for phosphorus in iron, and analysis of the strain-rate-sensitivity data shows that the same deformation models are applicable. Strong elastic interactions between phosphorus atoms and dislocations are believed to be responsible for the observed deformation behavior. Comparison of the present results with those obtained previously on Fe−P alloys and with data in the literature indicates that the strengthening resulting from phosphorus additions to steel is expected to be additive to other strengthening mechanisms.     

The microstructures and properties of an al- 12 wt pct

A new process for producing rapidly solidified bulk alloys was developed based on the hammer- and-anvil concept. In the process, an A1-12 wt pct Si alloy slab was built up layer by layer and then hot worked to get a solid and integral sheet. The oxygen content of the layer-deposited alloy is less than the typical value of powder metallurgy (PM) alloys by one order, and the cooling rate can reach 10⁴ K/s, which is higher than that of the spray deposition process. In comparison with the ingot-processed Al-12 wt pct Si alloy, layer-deposited alloy exhibits su- perior mechanical properties. This is attributable to the fine and uniform silicon-particle distri- bution which not only brings on dispersion hardening effect but also raises the elongation and fracture strain. The mechanisms responsible for this enhancement were discussed in terms of particle size and effective volume fraction.     

Processing and evaluation of 15Cr-15Mo nickel base superalloy

A Nickel base solid solution strengthened alloy has been made with a nominal chemical composition of 15Cr-15Mo (balance Ni) through vacuum melting route and was characterized in hot worked and heat-treated conditions. Processing parameters have been optimized to get the desired microstructure and mechanical properties. The alloy has shown very good mechanical properties at elevated temperatures as well as at cryogenic temperatures. Role of solution treatment temperature and correspondingly role of grain size on mechanical properties at different temperatures has also been evaluated and reported. Heat treatment cycle for application of alloy upto 700°C has been optimized. Properties of the alloy have been compared with similar class of alloys.