High-temperature Compressive Deformation Behavior Research Articles

High temperature compressive deformation behavior of an extruded Mg–8Gd–3Y–0.5Zr (wt.%) alloy

The deformation behavior of an extruded Mg–8Gd–3Y–0.5Zr alloy has been characterized by compression tests in the temperature range of 400–490°C and strain rate range of 10−4s−1 to 10−2s−1 with the objective to evaluate the superplastic deformation conditions as well as the rate-controlling mechanisms. The strain rate sensitivity index m decreases with increasing temperature in the strain rate range of 10−4s−1 to 5×10−4s−1, which was attributed to grain growth. Optimum superplasticity characterized by grain boundary sliding accommodated by dislocation creep was obtained at 400°C and at 10−4s−1. Dynamic precipitation leading to precipitates distributed mainly in the grain boundaries was responsible for the stable microstructure and the increase of the stress during deformation under this condition. Moreover, at strain rate higher than 5×10−4s−1, it remained relatively constant of about m≈0.3 and the activation energy Q was found to be equal to 131kJ/mol which was close to the activation energy for lattice diffusion of Mg.

Effects of temperature on dynamic compressive properties of Zr-based amorphous alloy and composite

This study investigates the high-temperature dynamic compressive deformation behavior of Zr-based amorphous alloy and amorphous matrix composite containing ductile β crystalline phases. Dynamic compressive tests were conducted in the temperature range from room temperature to 380 °C using a compressive Kolsky bar, and then the test data were analyzed in relation to microstructure and fracture mode. Dynamic compressive test results indicated that both the maximum compressive stress and the total strain of the amorphous alloy and composite decreased with the increasing test temperature because shear bands could propagate rapidly as the adiabatic heating effect was added at high temperatures. Above the glass transition temperature, total strain decreased more abruptly than that measured between the room temperature and 300 °C according to the crystallization of amorphous phases. The maximum compressive stress and the total strain of the amorphous composite were higher than those of the amorphous alloy in the overall test temperature range because β phases played a role in forming multiple shear bands. These findings suggested that applying the evaluation criteria for mechanical properties measured under room temperature quasi-static loading could cause risks when the Zr-based amorphous alloy and composite were used at high temperatures under dynamic loading conditions.

Deformation mechanism of quasicrystals

Characteristics of the high-temperature compressive deformation behavior of icosahedral and decagonal quasicrystals are reviewed. In icosahedral quasicrystals, the true stress versus true strain relation shows a pronounced yield drop, followed by gradual softening towards a minimum at a large true strain of about 0.5 and then changes to hardening at higher strain; the yield and flow stresses are quite sensitive to temperature and strain rate. In decagonal quasicrystals, the yield stress depends weekly on orientation in spite of its anisotropic structure. In both types of quasicrystals, the yield stress is higher in higher quality samples. The deformation mechanism of the quasicrystals is discussed in terms of dislocations glide in the quasicrystalline lattice governed by the Peierls mechanism. The Peierls mechanism in quasicrystals differs from that in crystals in that the dislocation glide is accompanied by a phason atrain relaxation and the Peierls potential is not periodic but quasiperiodic.

Elevated temperature compressive behavior of cast NiAl–9Mo(1Hf) eutectic alloys

The microstructure and mechanical behavior of NiAl–9Mo eutectic alloys with and without 1 at.% Hf have been investigated by using SEM, TEM and high temperature compressive tests, respectively. It was suggested that NiAl–9Mo–1Hf shows a significant strength advantage over NiAl–9Mo due to the presence of Heusler phase in the former alloy. Their high temperature compressive deformation behavior is proposed to be properly described by power-law equations.

High Temperature Compressive Deformation Behavior of Superplastic B, C-SiC

The nano-grained B,C-SiC was fabricated by hot-isostatic-pressing (HIP) at ultra-high-pressure. The average grain size of the SiC was 200 nm and the superplastic elongation over 100% was exhibited in tensile deformation. The high temperature compressive deformation behavior of the superplastic B,C-SiC was invcstigatcd. The compressive tests were conducted at the temperature range from 1600 to 1800°C at various strain rates from 3x10 -6 to 1x10 -4 s -1 . The some cracks were formed during the deformation of 30% at all test conditions. The specimen fractured without deformation at 1600°C at 1x10 -4 s -1 . The SEM observation after deformation revealed the equiaxed grain shape and the grain growth.

High-temperature slow-strain-rate compression studies on CoAI-TiB2 composites

CoAl-base composites containing various volume fractions of TiB2 particulates in the 1 to 3-μm size range were tested in compression over a range of strain rates at 1100 to 1300 K. Hotpressed and postcompression microstructures were characterized using optical and transmission electron microscopy. For a strain rate of 2 × 10-6 s-1, the flow stress at 1300 K of CoAl-20 vol pct TiB2 was twice that of monolithic CoAl. Correspondingly, the stress exponent of CoAl-20 vol pct TiB2 at 1300 K was ∼4.5 compared to ∼3.0 for stoichiometric monolithic CoAl. This increased resistance of the composite to deformation at elevated temperatures is attributed to TiB2 particulate-dislocation interactions. The high-temperature compressive deformation behaviors of NiAl-TiB2 and CoAl-TiB2 composites are compared.