Temperature Dependence Of Tensile Behavior Research Articles

Temperature dependence of tensile behavior, deformation mechanisms and fracture in nitrogen-alloyed FeMnCrNiCo(N) Cantor alloys

Among a family of the multi-principle-element alloys, a high-entropy Cantor alloy attracts much attention due to the striking temperature dependence of strength properties, strong grain boundary hardening and the excellent low-temperature ductility. Cantor alloy is a substitutional concentrated solid solution, thus, its strength properties and strain hardening could be additionally enhanced by interstitial hardening. Here we explore the effect of nitrogen alloying with atomic concentrations of 0.8%, 1.4% and 1.6% on a temperature dependence (temperature range from 77 to 473 K) of the microstructure, mechanical properties, and fracture micromechanisms of FeMnCrNiCo alloy with the focus on low-temperature deformation regime. Nitrogen-alloying promotes the expansion of a crystal lattice with a linear increase of a lattice parameter of the alloy with nitrogen content, ∆a/∆CN = 0.625 pm/at%. Nitrogen-bearing FeMnCrNiCo(N) alloys possess stronger temperature dependence of a yield strength relative to the Cantor alloy, and nitrogen forces both athermal and thermal components of the stress. The solid-solution strengthening of Cantor alloy is proportional to the nitrogen concentration Δτ ~ CN, and the value (ΔYS/ΔCN) for the coarse-grained FeMnCrNiCo(N) alloys is a temperature-dependent parameter (ΔYS/ΔCN = 97 MPa/at% at RT and ΔYS/ΔCN = 146 MPa/at% at 77 K). Dislocation slip is a dominating deformation mechanism of the nitrogen-alloyed alloys along the whole range of the deformation temperatures. A decrease in test temperature and nitrogen-alloying both force the tendency to the planar slip and facilitate strain hardening. Despite a weak effect of nitrogen on a stacking fault energy of the Cantor alloy and high deforming stresses in FeMnCrNiCo(N) alloys, nitrogen-containing alloys show low activity of the mechanical twinning. Opposite effects of the nitrogen-alloying on the elongation of the Cantor alloy were found for different deformation regimes: positive at T > 250 K (elongation increases with nitrogen-alloying) and negative at T < 250 K (it decreases in nitrogen-bearing alloys). For FeMnCrNiCo(N) alloys, the appearance of the ductile-to-brittle transition in low-temperature deformation regime is associated with the brittle intergranular fracture of the specimens alloyed with nitrogen CN ≥ 1.4 at%.

Temperature dependence of tensile behavior in poly(butylene terephthalate) with different crystallinity

The tensile behavior of PBT with different crystallinity was investigated at various temperatures. It turned out that the origin of stress whitening is different for PBT crystallized at 100°C and 180°C. The deformation of PBT crystallized at 100°C involves crazing/tearing and fibrillation at different temperatures. The complicated fracture morphologies including brittle fracture, fibrillation and ductile ploughing are linked to the temperature-dependent deformation mode of PBT crystallized at 180°C. The yield behavior could be described based on the Ree-Eyring model for PBT crystallized at 100°C and 180°C. The effect of temperature on Young's modulus, fracture strain and yield stress was analyzed and the fracture morphology was discussed in detail.

Temperature dependence of tensile behavior and deformation microstructure of a Re-containing Ni-base single crystal superalloy

Tensile behavior of a Re-containing Ni-base single crystal superalloy with [001] orientation was conducted at from room temperature to 1100°C, and the corresponding deformation microstructure after fracture has been investigated by TEM. This alloy exhibits temperature dependent deformation microstructure and resultant tensile behavior. Shearing of γ' precipitates by dislocations, with respect to anti-phase boundary (APB) shearing and superlattice stacking fault (SSF) shearing, is mainly controlled by the interplay between γ/γ' lattice misfit, intrinsic strength of γ' phase and stress field of dislocations accumulated on γ/γ' interfaces. Below 800°C, the variation with temperature of (0.2%) yield strength is closely linked with the way of dislocations entering γ' precipitates, which is largely influenced by temperature dependent γ-γ' microstructure modifications. The tensile strength at 1100°C is determined by gliding-climbing of dislocations, with the help of thermal activation, in obviously modified γ-γ' microstructure. In fact, flow stresses at 800°C and 1100°C drop remarkably with the onset of numerous APB shearing of γ' particles after γ/γ' misfit stresses are relaxed by depositing dislocations. Last, thermally-activated and plasticity-induced γ-γ' microstructure modifications are taken into account to elucidate the deformation microstructure and resulting tensile behavior of this Re-bearing alloy at various temperatures.

Effect of temperature on tensile behavior of Ni–Cr–W based superalloy

The temperature dependence of tensile behavior of Ni–Cr–W based superalloy has been studied by tensile tests in the temperature range of 25–900 °C. The results indicated that the yield strength was anomaly with increasing temperature. Below 600 °C, both the tensile and yield strength decreased slightly with increasing temperature; above 600 °C, the tensile strength decreased rapidly while the yield strength almost kept invariable; the elongation had its minimum value at 600 °C. Microstructure analysis showed that M 23C 6 carbides including of lamellar carbides (600 °C) and discrete carbides (above 600 °C) precipitated at the grain boundaries. The lamellar M 23C 6 carbides with the width of 1–3 μm weakened the strength of grain boundary, and thus led to the premature failure of the alloy. But the grain boundary sliding was effectively restricted by discrete M 23C 6 carbides. TEM analysis showed that the high dislocation density and cross-slip also contributed to the yield strength anomalous.

Temperature dependence of tensile behavior of a high nitrogen Fe–Cr–Mn–Mo stainless steel

Temperature dependence of tensile behavior of a high nitrogen Fe–Cr–Mn–Mo stainless steel with nitrogen content of 0.66% was investigated. It was found that strength of the steel increased with decrease of temperature, and the deformation microstructure of the steel which determines the strain-hardening behavior was strongly dependent on temperature. It was analyzed that stacking fault energy (SFE) of the steel decreased with decrease of temperature, which promoted the twinning and planar slipping in the steel, and thus made brittle fracture to occur at cryogenic temperature.

Temperature dependence of tensile behavior of Ni-based superalloy M951

Tensile properties of M951 alloy are shown to be significantly dependent on temperatures in this study. Like in other superalloys, the yield and tensile strengths decreased slightly between room temperature and 600 °C, then both strengths showed peak values at intermediate temperatures, and both decreased sharply above 850 °C. The elongation fluctuated with temperature with its minimum at 800 °C. The TEM observations showed that at low temperature the dominant deformation mechanism was γ′ shearing by dislocation pairs and slip bands. At high temperature, the deformation was dominated by γ′ by-pass. At intermediate temperature it showed a transition from γ′ shearing to by-passing.

Atomistic simulations of the size, orientation, and temperature dependence of tensile behavior in GaN nanowires

Molecular dynamics simulations with Stillinger-Weber potentials were used to study the response of wurtzite-type single-crystalline GaN nanowires to a tensile strain along the axial direction. Nanowires with axial orientations along the [0001], $[1\overline{1}00]$, and $[11\overline{2}0]$ crystallographic directions, which correspond to experimentally synthesized nanowires, were studied. The results reveal that the nanowires with different axial orientations show distinctly different deformation behaviors under loading. The brittle to ductile transition (BDT) was observed in the nanowires oriented along the [0001] direction and the BDT temperatures lie in the temperature range between 1500 and $1800\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The nanowires oriented along the $[11\overline{2}0]$ direction exhibit slip in the ${01\overline{1}0}$ planes, whereas the nanowires oriented along the $[1\overline{1}00]$ direction fracture in a cleavage manner under tensile loading. It should be emphasized that multiple yield stresses were observed during different stages in the $[11\overline{2}0]$-oriented nanowires. In general, Young's modulus of the GaN nanowires decreases with decreasing diameter of the nanowires.