Low-temperature elastic properties of a 300-grade maraging steel

Elastic properties of an annealed 300-grade maraging steel (18 Ni, 9 Co, 5 Mo pct by weight) were studied between room temperature and liquid-helium temperature. Longi-tudinal and transverse ultrasonic velocities were determined by a pulse method. The re-ported elastic constants are: longitudinal modulus, shear modulus, Young’s modulus, bulk modulus, and Poisson’s ratio. Except for the bulk modulus, the room-temperature elas-tic constants are all lower than those of iron; and their temperature dependencies are regular in the studied temperature region.     

Elastic constants of some transition- metal- disilicide single crystals

The elastic constants,c _ij, of VSi₂ (C40), CrSi₂ (C40), TiSi₂ (C54), and CoSi₂ (Cl) single crystals were determined at room temperature from the velocities of ultrasonic waves. The orientation dependence of the compliance constants, s₁₁ and s₆₆, and Poisson’s ratio were discussed for each disilicide single crystal. Elastic moduli like Young’s modulus of ideal polycrystalline com-pounds were estimated from the elastic constants of single crystals using Hill's approximation. The elastic moduli of the disilicides are higher than those of the constituent elements, except for CoSi₂. CoSi₂ shows a higher Poisson’s ratio of 0.36 compared with that of the other dis-ilicides, 0.15 to 0.19. The Young’s modulus and the shear modulus of the disilicides increase with increasing melting temperature, and these are located in the upper part of the band indi-cating the elastic moduli-melting temperature relationship in intermetallic compounds. TiSi₂, VSi₂, CrSi₂, and MoSi₂ exhibit considerably higher Young’s modulus to density ratio, about 70 GPa/(g/cm³), than the constituent elements, except for Si     

Elastic moduli of titanium-hydrogen alloys in the temperature range 20 °C to 1100 °C

The elastic properties of a series of polycrystalline titanium-hydrogen alloys (containing up to 25 at. pct H) were measured over the temperature range 20 °C to 1100 °C. The latter limits permitted investigation of adjacent parts of the α+δ, α, and β phase fields. A laser ultrasonic technique was employed to measure the temperature and hydrogen-concentration dependencies of the elastic constants. The room-temperature elastic properties of the alloys depended only slightly on hydrogen concentration, remaining almost independent of the volume fraction of the δ hydride phase. In the α phase field, the addition of hydrogen decreased the shear and Young’s moduli and increased the bulk modulus, Lamé constant, and Poisson’s ratio. The Young’s and shear moduli decreased more rapidly with increasing temperature than in cubic phases. By contrast, Poisson’s ratio increased with temperature. In the β phase field, the temperature dependence of the elastic constants was weak. However, alloying with hydrogen increased the shear and Young’s moduli, decreased Poisson’s ratio, but did not appreciably affect the bulk modulus and Lamé constant. The different effects of hydrogen on the elastic constants of alpha and beta titanium are interpreted in terms of the influence of dissolved hydrogen on the stability of the hexagonal close-packed (hcp) and body-centered cubic (bcc) lattices in the vicinity of the α-to-β transformation. The present results are also used to help account for the effect of hydrogen concentration on the mechanical properties of Ti-H alloys.     

Damage effect on the fracture toughness of nodular cast iron: Part I. Damage characterization and plastic flow stress modeling

After chemical, morphological, and mechanical characterization of ductile cast iron, the damage mechanisms were studied by tensile tests inside the scanning electron microscope (SEM). The evolutions of Young’s modulus and of Poisson’s ratio were measured in uniaxial tensile tests. Compression tests were used to measure the pressure sensitivity coefficient of the flow stress. The damage is produced by early initiation of cavities at the pole cap of graphite nodules by debonding of the interface, followed by the growth of cavities. The mechanical behavior was modeled in the elastic region by calculating the Hashin-Shtrickman bounds. This provided the elastic constants for the graphite nodules. The plastic behavior was modeled by considering that the graphite nodules were replaced by voids. The critical interfacial stress for debonding was determined by analytical as well as by finite-element calculations. The growth rate of cavities was deduced from the evolution of the Poisson’s ratio and was compared with predictions from Gurson’s potential. The stress-strain behavior could be modeled either by extension of the Mori-Tanaka analysis in the plastic range or by finite-element computations. This allowed a fair prediction of the observed behavior.     

Prediction of properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-C refractory based on microstructure by an improved generalized self-consistent scheme

An improved generalized self-consistent scheme (GSCS), which has a simplified computation process, was proposed to predict the properties, based on microstructure, of multiphase materials. The results of the prediction of the elastic modulus, Poisson’s ratio, coefficient of thermal expansion, and coefficient of thermal conductivity of an Al₂O₃-C refractory using a multiscale homogenization method with this improved GSCS agree with the experimental results. It is found that understanding the microstructure and choosing a suitable matrix for the prediction are very important for prediction accuracy.     

Correction

Elastic moduli and tensile and physical properties were measured at room temperature on texture-free powder metallurgical (PM) Ti-6Al-4V alloy as a function of heat treatment and quenching (HTQ) from temperatures between 600 °C and 1200 °C. The elastic moduli and other physical properties, which are often regarded to be constant, were found to depend strongly on heat treatment. The property variations are interpreted on the basis of the phases and phase volume fractions which are controlled by HTQ. For example, soft metastable (beta/alpha′) phase formed by 800 °C HTQ induces the lowest values of yield strength and Young’s modulus. Alpha + beta microstructures are associated with a low Poisson’s ratio of 0.27, while alpha′ microstructures have a high Poisson’s ratio between 0.35 and 0.36. Several other mechanical and physical properties are derived from the measured properties. Formerly Research Associate, Institute for Materials Research, German Aerospace Research Establishment The online version of the original article can be found at     

Elastic moduli and tensile and physical properties of heat-treated and quenched powder metallurgical Ti-6Al-4V alloy

Elastic moduli and tensile and physical properties were measured at room temperature on texture-free powder metallurgical (PM) Ti-6Al-4V alloy as a function of heat treatment and quenching (HTQ) from temperatures between 600 °C and 1200 °C. The elastic moduli and other physical properties, which are often regarded to be constant, were found to depend strongly on heat treatment. The property variations are interpreted on the basis of the phases and phase volume fractions which are controlled by HTQ. For example, soft metastable (beta/alpha′) phase formed by 800 °C HTQ induces the lowest values of yield strength and Young’s modulus. Alpha + beta microstructures are associated with a low Poisson’s ratio of 0.27, while alpha′ microstructures have a high Poisson’s ratio between 0.35 and 0.36. Several other mechanical and physical properties are derived from the measured properties. Formerly Research Associate, Institute for Materials Research, German Aerospace Research Establishment An erratum to this article is available at .     

Ductile Ti-Based Bulk Metallic Glasses with High Specific Strength

Ti-based bulk metallic glasses (BMGs) with large compressive plasticity were developed in the Ti-rich part of Vitreloy series BMGs (Ti_65–x Zr _x Cu₉Ni₈Be₁₈ alloys with x = 0, 5, 10, 15, and 20). The current materials exhibit high fracture strength reaching ~2.3 GPa and plastic strains up to ~8.3 pct after partial substitution of Zr by Ti. The plasticity of the investigated alloys strongly depends on the Zr content, which affects the elastic constants, such as Poisson’s ratio and shear modulus. This, in turn, has an impact on the shear transformation zone (STZ) volume and, hence, on the shear banding of the glasses.     

Electronic origin of elastic properties of titanium carbonitride alloys

We have carried out numerical ab initio calculations of the elastic constants for several cubic ordered structures modeling titanium carbonitride (TiC_xN_1−x) alloys. The calculations were performed using the full-potential linear augmented plane-wave method (FPLAPW) to calculate the total energy as functions of volume and strain, after which the data were fit to the traditional Murnaghan equation of state and to a polynomial function of strain to determine the formation energy; the bulk modulus; and the elastic constants C ₁₁, C ₁₂ and C ₄₄. The predicted equilibrium lattice parameters are slightly higher than those found experimentally (on average by 0.2 pct). The computed formation energy indicates that the alloys are stable in the entire range of the carbon concentration x and the maximum stability is obtained for 0.5≤x≤0.75. The computed bulk modulus, the shear modulus G, and the Young’s modulus E are within approximately 2, 1, and 2 pct of the experimentally measured characteristics, respectively. The maximum deviation is observed for TiC and TiN. The moduli G, E, and Poisson’s ratio reach a maximum value at approximately the middle of the concentration range, which is due to the fact that the shear modulus C ₄₄ shows a maximum value for a valence electron concentration (VEC) in the range of 8.25 to 8.5. The other shear modulus (C ₁₁−C ₁₂)/2 does not exhibit any maximum overall concentration range and instead has a flat dependence in the range mentioned previously. Such a concentration behavior of the elastic constants is related to specific changes in the band structure of TiC_xN_1−x alloys caused by the orthorhombic and monoclinic strains that determine the shear moduli (C ₁₁−C ₁₂)/2 and C ₄₄, respectively. This article is based on a presentation made in the symposium entitled “Fourth International Alloy Conference”, which occurred in Kos, Greece, from June 26 to July 1, 2005, and was sponsored by Engineering Conferences International (ECI) and co-sponsored by Lawrence Livermore National Laboratory and Naval Research Laboratory, United Kingdom.     

Elastic constants of binary iron-base alloys

The Young’s modulus (E) and shear modulus (G) of isotropic Fe and binary Fe-C, Fe-Co, Fe-Cr, Fe-Ir, Fe-Mn, Fe-Ni, Fe-Pt, Fe-Re, Fe-Rh, and Fe-Ru alloys have been determined as functions of composition (0 to 10 at. pet) and temperature (77 to 473 K) by a pulse-echo technique (100 kHz elastic waves). Poisson’s ratio (v) and the bulk modulus (K) have been derived from the values of E and G. The rates of change of E and G with composition (ΔE/Δc and ΔG/Δc) depend on the change of lattice parameter with composition and upon the position of the solute in the periodic table. Both negative and positive values of ΔE/Δc and ΔG/Δc are observed. The values of ΔE/Δc and ΔG/Δc are generally different so that Poisson’s ratio may increase or decrease with composition. Comparable changes in the value ofK/G also occur. These changes cannot be used to predict the effects of alloying additions on the toughness of iron. The temperature dependence of E andG of the alloys is similar to that of iron, decreasing in a nonlinear manner from 77 to 473 K.     

Temperature and composition dependence of the elastic constants of Ni3Al

The stiffness constants, c _ij , of monocrystalline Ni₃Al of three different compositions, 23.2, 24.0, and 25.0 at. pct Al, were measured over the temperature range from 300 to 1100 K using the rectangular parallelepiped resonance (RPR) method. The bulk modulus, as well as the shear modulus, Young’s modulus, and Poisson’s ratio for randomly oriented polycrystalline stoichiometric Ni₃Al, were derived from the stiffness constants. The data indicate that c ₄₄ is essentially independent of composition, decreasing slightly with increasing temperature for all three alloys. The values of c ₁₁ and c ₁₂, however, decrease with increasing aluminum content, the difference being small at room temperature but becoming larger at higher temperatures. We find that c ₁₁ and c ₁₂ are not as sensitive to aluminum concentration as is implied by previous results. A comparison of different shear moduli of Ni₃Al and the saturated Ni-Al solid solution in equilibrium with it indicates that the ordered phase is generally elastically stiffer than the solid solution over the range of temperatures at which coarsening of the Ni₃Al precipitate has been heavily investigated.     

Temperature dependence of the Young’s modulus and shear modulus of pure nickel,platinum, and molybdenum

A pulse-echo technique utilizing a wave guide operating at high temperatures has been used to measure the variation in the Young’s modulus and shear modulus of pure platinum, nickel, and molybdenum in the temperature range from 25 to 1000°. With the exception of Ni in the temperature range below the Curie point, linear behavior was found for all three metals. The significance of the linear relation between temperature and the elastic constants for Mo to the observed nonlinearity of the Arrhenius plot of the diffusivity of carbon in Mo is discussed.     

Time-temperature-precipitation characteristics of high-nitrogen austenitic Fe−18Cr−18Mn−2Mo−0.9N steel

The time-temperature-precipitation (TTP) and corresponding mechanical properties in high-nitrogen austenitic Fe−18Cr−18Mn−2Mo−0.9N steel (all in weight percent) were investigated using electron microscopy and ambient tensile testing. The precipitation reactions can be categorized into three stages: (1) high-temperature region (above 950°C)—mainly coarse grain-boundary (intergranular) Cr₂N; (2) nose-temperature region—integranular Cr₂N→cellular Cr₂N→intragranular Cr₂N+ sigma (σ); and (3) low-temperature region (below 750°C)—intergranular Cr₂N→cellular Cr₂N→ intragranular Cr₂N+σ+chi(χ)+M₇C₃ carbide. After cellular Cr₂N precipitation became dominant above 800°C, yield and tensile strength gradually decreased, whereas elongation abruptly deteriorated with aging time. On the contrary, prolonged aging in the low-temperature regime increased tensile strength, caused by the precipitation of fine χ and M₇C₃ within grains. Based on the analyses of selected area diffraction (SAD) patterns, the crystallographic features of the second phases were analyzed.     

Precipitation Kinetics of Cr2N in High Nitrogen Austenitic Stainless Steel

The precipitation behavior of Cr2 N during isothermal aging in the temperature range from 700 ℃ to 950 ℃ in Fe-18Cr-12Mn-0.48N （in mass percent） high nitrogen austenitic stainless steel, including morphology and content of precipitate, was investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The isothermal precipitation kinetics curve of Cr2 N and the corresponding precipitation activation energy were obtained. The results show that Cr2N phase precipitates in a cellular way and its morphology is transformed from initial granular precipitates to lamellar ones in the cell with increasing aging time. The nose temperature of Cr2 N precipitation is about 800 ℃, with a corresponding incubation period of 30 min, and the ceiling temperature of Cr2N precipitation is 950℃. The diffusionactivation energy of Cr2 N precipitation is 296 kJ/mol.     

An analysis of the mechanical behavior of Al-Al3Ni composites

Commercial purity Al-Al₃Ni eutectic composites have been prepared by directional solidification at growth rates ranging from 9.63 x 10^-3 to 1.0 mm/s. The composites were tested in tension and in compression and the results were analyzed using a simple model taking into consideration the difference in Poisson’s ratio of the phases, interfiber spacing, and discontinuity and premature fracture of fibers. The theoretically predicted values of the tangent modulus and strength in tension and compression were shown to closely fit the experimental results up to a growth rate of about 0.3 mm/s. Beyond this value, the excessive misalignment of the fibers caused some deterioration in the mechanical properties and a change in the mode of fracture. It has been concluded that the elastic constrained matrix exerts considerable effect on the mechanical properties thus providing an effective means of improving them by increasing the surface area of the fiber-matrix interface.     

The loss of driving force due to volume diffusion ahead of a migrating boundary in a cellular precipitation reaction

Experimental confirmation has been obtained of the existence of a solute diffusion zone ahead of a migrating cell boundary during the cellular precipitation of Cr₂N in a high nitrogen CrNi austenitic steel. The solute profile has been measured directly using analytical electron microscopy and indirectly by optical microscopy of potentiostatically etched specimens. The width of the diffusion zone was observed to increase with reaction time; this corresponded to the deceleration of the migration rate of the cell boundary with reaction time.     

The relationship between chromium nitride and secondary austenite precipitation in duplex stainless steels

A detailed investigation of the early stages of secondary austenite precipitation in five duplex stainless steel (DSS) commercial alloys (UNS S32304, S32205, S32550, S32750, and S32760) has been conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on this study, a model is proposed that describes the interaction betwee Cr₂N and austenite (intergranular and intragranular) precipitation in these alloys. Depending on nitrogen availability and interface mobility, Cr₂N precipitation along existing ferrire/austenite interfaces precedes intergranular secondary austenite growth. The low-energy interfaces formed between the Cr₂N, the ferrite, and the austenite, along with the coupled diffusion processes, are the factors controlling this phase transformation. Finally, in the case of the intragranular nitrides, a mechanism is proposed whereby the nitrides serve as sites for heterogeneous nucleation of intragranular secondary austenite.     

Electron microscopic study of cr2n formation in thermally aged 316ln austenitic stainless steels

The formation of dichromium nitride phase in low nitrogen austenitic stainless steels has been studied by transmission electron microscopy (TEM). The electron diffraction patterns unambiguously confirm the formation of Cr₂N phase on aging these steels in the range of 1023 to 1123 K, for time durations up to 100 hours. It is found that while no perceptible microstructural features could be recognized, formation of dislocation pairs is an important characteristic that could be associated with the nitrogen ordering in the matrix. The precipitation sequence processes have been discussed on the basis of stress-induced interactions that are predominant in interstitial alloys. Further, certain aspects of me-chanical behavior are explained on the basis of our study.