HIPed Specimens Research Articles

Mechanical Behavior of L12 Single Crystal AI66Ti25Mng

Single crystal AI66Ti25Mng has been produced and tested in compression as a function of temperature and orientation. Yield strengths for orientations near [001] and [111] continuously decrease with increasing temperature in a manner similar to other single crystal L12 trialuminides, and also to polycrystals of these materials. Slip was determined to occur on the {111} octahedral planes using two-surface analysis. Critical resolved shear stress (CRSS) variation with temperature, calculated on {111} planes, overlap closely for both orientations. Dislocation analysis confirmed the Burgers vectors to be of the type a at both 298K and 1073K. A limited number of uniaxial tension tests were conducted near [001] at 1073K; the HIPed specimens contained a small amount of residual porosity and second phases which resulted in lastic failure even at this high temperature.

Effect of HIPing on Defect and Strength Characteristics in Y-TZP

The effects of HIPing on the defect size distribution and the mechanical properties of ceramics were examined. Specimens of Y-TZP were HIPed under several conditions. Microstructures of the specimens were observed by SEM. The defect size and number were directly measured by transmission optical microscopy. The fracture toughness was measured by SEPB method. In all specimens, larger number of defects exist in the range of smaller defect size. Total number of defects and the largest defect size were reduced by HIPing. However, even in HIPed specimens, there are a few defects having several tens micrometers long. The fracture origin appeared to change from the bulk defects to the surface ones with reduction of the total defect number and the largest defect size by HIPing.

Effect of Isostatic GAS Pressure on Optical Quality of MgAl2O4 Spinel

ABSTRACTOptical transparent MgAl2O4 spinel is obtained by processing with high gas pressure to eliminate or reduce the residual pores. Both hot–pressed and sintered specimens are post–treated by the high argon hipping process here. The densities of all the specimens before hipping are over 99% theoretical density. In the high gas pressure process, the pressure ranges from 2000 to 30000psi at 1500°C for 2hrs. The transmittance from visible to IR are measured before and after gas pressure treatment. The transparency from visible to IR increases significantly with the HIP process. When applied pressure less than 6000psi, bulk density is proportional to the logarithm of the pressure and the logarithm of the absorption coefficient is proportional to the porosity. Bimodal grain–size distribution exists in the sintered and hipped specimens but is not observed in the uniaxial–hot–pressed–only samples. XRD analysis indicates the width of the diffraction peaks in the HIP specimens is less than that in UAHP specimens. The result illustrates the HIP process improves the spinel crystallinity.

High-cycle fatigue Behaviour of iron-based PM-materials

The effect of pores and inclusions on the high-cycle fatigue and threshold behaviour of PM iron and PM steel specimens containing porosities of up to 22% has been investigated. HIPed specimens have been prepared to obtain base-line data from practically pore-free materials. The distribution, size and morphology of the inhomogeneities was characterised as function of porosity by quantitative metallography and fractography, in addition to measurements of the Young's modulus and the electrical resistivity. The results show that the properties for low-porosity material can be interpreted on the basis of the appropriate Kitagawa-diagram, taking into account the effective threshold stress intensity and the magnitude and extent of the stress concentration at the perimeter of the pores or inclusions. For high-porosity material the properties appear to be related to the actual load-bearing area, ie the sum of the cross-sections of the fractured sintering necks as revealed by fractography.

Mechanical Properties of Fe-Modifie Ll2-Type Al3Ti

ABSTRACTThe room temperature ductility of an L12-type A13Ti alloy containing 7.5 at.% Fe has been improved substantially by hot isostatic pressing (HIP) after arc casting. This L12-type alloy can be deformed in compression to 11.4 % at room temperature after HIPing, retaining the original shape of compressive specimens, while compressive specimens without HIPing following heat-treatment for homogenization (HHT) fracture into small pieces when deformed to similar strain. At temperatures higher than 400°C, specimens for both HHTed and HIPed conditions show similar behavior, having strains to failure of greater than 12 % plastic strain. Fracture occurs at room temperature by brittle transgranular cleavage with a smooth surface in HHTed specimens, while in HIPed specimens, fracture occurs by both transgranular and intergranular modes. Transgranularly fractured surfaces in the latter case have rough surfaces with fine structure, indicating ductile fracture as compared with that for HHTed specimens. In both HIPed and HHTed specimens, no fracture surfaces are flat and parallel to any crystallographic planes. High resolution electron microscopy has revealed that a pair of superlattice partial dislocations on a (111) plane have a spacing of approximately 11 nm (2–3 times larger than that for Al-23Ti-6Fe-5V) giving an antiphase boundary energy of 95 mJ/m2. Since this energy is relatively low, the present alloy may be ductile because of its ready emission of dislocations at crack tips, according to the Rice-Thomson criterion. Improvement of room-temperature ductility of this alloy is attributed primarily to the reduction of a large population of cavities formed upon arc casting.

Microstructure and Mechanical Properties of Sintered TiAl

Pulverised TiAl powder was cold isostatically pressed at 392 MPa and the resulting compact sintered at temperatures up to 1623 K to produce sintered TiAl with relative densities as high as 91%. This process formed a laminated structure consisting of TiAl and Ti3AI, which gave a high compressive yield strength accompanied by embrittlement of the sintered TiAl compacts, no bending plastic deformation being observed at room temperature. When centrifugally atomised powder melted in a CaO crucible was used, sintered TiAl specimens, apparently of full theoretical density, could be obtained by canned hipping at 1473 K under a pressure of 98 MPa. The hipped TiAl specimens had a grain size of ~20–30 μm, and grain coarsening was not observed, even when specimens were annealed for 720 ks at temperatures of 1273–1373 K. Hipped specimens annealed at 1273 K had a yield strength of 388 MN m −2 at room temperature, and bending ductilities > 0·4% were obtained. PM/0426