Elevated Temperature Compressive Behavior Research Articles

Elevated temperature compressive behavior of a beryllium-aluminum casting alloy

The performance of elevated temperature compressive deformation of the beryllium-aluminum casting alloy was investigated in the temperature range of 450–660 °C and strain rate 0.1–50 s−1. The temperature mainly affects the load bearing ability and flowability of aluminum and thus the compatible plastic deformation of the alloy, while the strain rate mainly affects the work hardening effect and peak stresses. The deformation mechanism was discussed by combining analysis of the stress-strain curves and microstructures. The constitutive equation relating flow stress, strain rate, and deformation temperature of the alloy is established.

Elevated temperature compressive behavior of Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf alloy with minor Ho addition

Abstract The microstructure and elevated temperature compressive behavior of Nb-22Ti-16Si-7Cr-3Al-3Ta-2Hf alloys with and without 0.1 at.% Ho were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and compression tests. The results show that the addition of 0.1 at.% Ho to the matrix alloy significantly increases its elevated temperature strength at a higher strain rate, while the strengthening effect becomes weak at a lower strain rate. The elevated temperature compressive deformation behavior of the Ho-doped alloy can be adequately described by the power-law equation. The mechanism of Ho addition on elevated-temperature compressive behavior of the alloy is discussed in the paper.

Microstructural changes of SiCw/6061Al composite during compression at temperatures below and above the solidus of the matrix alloy

Elevated temperature compressive behavior of a 6061 aluminum alloy matrix composite reinforced with 20 vol.% β-SiC whisker was investigated at the strain rate from 0.016 to 1.0 s −1. The deformation temperatures were below and above the solidus temperature of the composite, which was determined by differential scanning calorimeter (DSC). It was found that the flow stress of the composite decreased with increasing compressive temperature. The superplasticity occurred in the composite during compression at 580 °C with the strain rate 0.37 s −1. The microstructure comprising whisker distribution and dislocation density of the matrix as well as interfacial reaction between the matrix alloy and the whisker of the composite before and after compression was observed and analyzed by using SEM and TEM.

Microstructure, brittle–ductile transition temperature and elevated temperature compressive behavior of the directionally solidified NiAl–Cr(Mo)–Hf alloy

The directionally solidified NiAl–27Cr–5.6Mo–0.4Hf (at.%) alloy was hot isostatically pressed at 1573 K, 100 MPa for 2 h and then annealed at 1323 K for 40 h. Microstructure examination revealed that the present alloy was mainly composed of three phases, i.e. the NiAl matrix, the lamellar Cr(Mo) and Heusler phase (Ni 2 AlHf). The interfaces between the NiAl–Cr(Mo), the NiAl–Ni 2 AlHf were atomically flat. The mechanical properties including the brittle–ductile transition temperature and the high temperature compressive behavior were also tested. The BDTT of the alloy was about 1233 K at a strain rate of 1.04 × 10 −4 s −1 and dependent on strain rate. This strain-rate dependent BDT can be explained by the cooperative dislocation generation model. The investigation on the high temperature compressive behavior between 1200 and 1300 K showed that the deformation behaviors of the alloy could be adequately described by the standard power-law. The possible strengthening mechanism was discussed.

Microstructure, brittle–ductile transition temperature and elevated temperature compressive behavior of the directionally solidified NiAl–Cr(Mo)–Hf alloy

The directionally solidified NiAl-27Cr-5.6Mo-0.4Hf (at.%) alloy was hot isostatically pressed at 1573 K, 100MPa for 2h and then annealed at 1323 K for 40 h. Microstructure examination revealed that the present alloy was mainly composed of three phases, i.e. the NiAl matrix, the lamellar Cr(Mo) and Heusler phase (Ni2AlHf). The interfaces between the NiAl-Cr(Mo), the NiAl-Ni2AlHf were atomically flat. The mechanical properties including the brittle-ductile transition temperature and the high temperature compressive behavior were also tested. The BDTT of the alloy was about 1233 K at a strain rate of 1.04 x 10(-4) s(-1) and dependent on strain rate. This strain-rate dependent BDT can be explained by the cooperative dislocation generation model. The investigation on the high temperature compressive behavior between 1200 and 1300 K showed that the deformation behaviors of the alloy could be adequately described by the standard power-law. The possible strengthening mechanism was discussed. (C) 2004 Elsevier B.V. All rights reserved.

Microstructure and elevated temperature mechanical behavior of cast NiAl–Cr(Mo) alloyed with Hf

An NiAl–Cr(Mo) alloy modified with Hf was fabricated by vacuum induction, melted and drop cast and then was hot isostatically pressed (HIPed) at 1523 K, 200 MPa for 4.5 h. The alloy was mainly composed of NiAl matrix, Cr(Mo) and Hf-rich phase distributed on the NiAl and Cr(Mo) phase boundary. The NiAl–Cr(Mo) and NiAl–Ni2AlHf interfaces were also investigated. Its elevated temperature compressive behavior was studied and the deformation features of the alloy could be adequately described by standard power-law which is usually used to characterize creep behavior for various metallic materials. The stress exponent n as well as the activation energy Q was calculated by fitting the experimental data to the power-law and temperature-compensated power-law equation. The possible strengthening mechanism was also discussed. Because the alloy had relatively high tensile strength, the tensile creep was performed at 1373 K and, as concluded from the stress component of different testing methods, the creep behavior may not be influenced by the testing method.

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.

Elevated temperature compressive behavior of in-situ multiphase composites NiAl/Cr(Mo)–TiC

A new multiphase composite based on intermetallic NiAl was fabricated using reaction synthesis method. The TiC particles were formed in-situ in the matrix and most of them accumulated at phase or grain boundaries. Its elevated temperature compressive behavior was investigated. The flow stresses of the composites generally decreased with increasing temperature and/or decreasing initial strain rate. It was found that the deformation feature of the composites could be adequately described by standard power law which is usually used to characterize creep behavior for various metallic materials. Thus the stress exponent n as well as activation energy Q were calculated by fitting the experimental data to the power-law and temperature-compensated power-law equations. The deformation behavior was discussed in comparison with other NiAl matrix composites. The high temperature strengths of the composites, especially the 16wt.%TiC particulate reinforced one, are superior to monolithic NiAl and a composite NiAl–20vol.%TiB2 at slower strain rate. The strengthening mechanisms were discussed preliminarily. However, when compared with directionally solidified NiAl/Cr(Mo), the present composites are relatively weak. An explanation for the weakness is given in the paper.