Evolution of the Microstructure and Mechanical Properties of a Ti35Nb2Sn Alloy Post-Processed by Hot Isostatic Pressing for Biomedical Applications

The HIP post-processing step is required for developing next generation of advanced powder metallurgy titanium alloys for orthopedic and dental applications. The influence of the hot isostatic pressing (HIP) post-processing step on structural and phase changes, porosity healing, and mechanical strength in a powder metallurgy Ti35Nb2Sn alloy was studied. Powders were pressed at room temperature at 750 MPa, and then sintered at 1350 °C in a vacuum for 3 h. The standard HIP process at 1200 °C and 150 MPa for 3 h was performed to study its effect on a Ti35Nb2Sn powder metallurgy alloy. The influence of the HIP process and cold rate on the density, microstructure, quantity of interstitial elements, mechanical strength, and Young’s modulus was investigated. HIP post-processing for 2 h at 1200 °C and 150 MPa led to greater porosity reduction and a marked retention of the β phase at room temperature. The slow cooling rate during the HIP process affected phase stability, with a large amount of α”-phase precipitate, which decreased the titanium alloy’s yield strength.

Effects of hot isostatic pressing and heat treatments on structural and corrosion properties of direct metal laser sintered parts

Purpose This paper aims to investigate the effects of various heat treatments on microstructure, hardness, porosity and corrosion properties of the parts. Design/methodology/approach Hot isostatic pressing (HIP) process, various heat treatments and their combinations were applied to the AlSi10Mg parts produced by direct laser metal sintering (DMLS). Findings It has been found that the HIP process, which is a post-processing process, reduces the amount of porosity in DMLS-AlSi10Mg material, thus improves corrosion resistance significantly. Originality/value In this study, the HIP process and subsequent T6 heat treatments were applied to AlSi10Mg parts produced by the DMLS technique. The study aims to increase the corrosion resistance of AlSi10Mg parts by reducing porosity with the HIP process and by altering the microstructure with the T6 process.

Evolution of the Microstructure and Mechanical Properties of a Ti35Nb2Sn Alloy Post-Processed by Hot Isostatic Pressing for Biomedical Applications

The influence of the hot isostatic pressing (HIP) post-processing step on structural and phase changes, porosity healing and mechanical strength in a powder metallurgy Ti35Nb2Sn alloy was studied. Powders were pressed at room temperature at 750 MPa, and then sintered at 1,350°C in a vacuum for 3 h. The standard HIP process at 1,200°C and 150 MPa for 3 h was performed to study its effect on a Ti35Nb2Sn powder metallurgy alloy. The influence of the HIP process and cold rate on density, microstructure, the quantity of interstitial elements, mechanical strength and Young's modulus was investigated. HIP post-processing for 2 h at 1,200°C and 150 MPa led to greater porosity reduction and a marked retention of the β phase at room temperature. The slow cooling rate during the HIP process affected phase stability, with a large amount of α”-phase precipitate, which decreased the titanium alloy’s yield strength.

Degradation and Corrosion of Biodegradable Metal Zn-xCa

Zn-based biodegradable metals (BMs) are considered as new potential in osteosynthetic implant devices. In this study Ca, which acts as an essential element in the human body, is used to improve the rate of Zn degradation and corrosion. The alloy was synthesized using the powder metallurgy method with two different processes: cold pressing followed by sintering (CP-S) and hot isostatic pressing (HIP). Microstructure properties, as well as in vitro degradation and corrosion were studied to determine the effect of adding Ca. Variations in the sample consist of Zn-0.5Ca, Zn-1Ca, Zn-1.5Ca and Zn-2Ca. The results and analysis of test data show that the addition of Ca increases the rate of corrosion and degradation of the materials. Better bonding and microstructure properties are obtained in Zn-2Ca samples which form CaZn13 phases and small porosity. As for the HIP process, a better microstructure is obtained compared to CP-S.

Measurement of residual strain in tantalum-clad tungsten after hot isostatic pressing

Tantalum-clad tungsten targets are a popular choice for spallation neutron production, due to the combination of high neutron yield and corrosion resistance. Such targets typically use the Hot Isostatic Press (HIP) process to bond the cladding to the core; this produces a strong bond but also introduces large residual stresses in the target and cladding. This is of particular interest at the ISIS neutron source, because cladding breaches are currently believed to limit the lifetime of ISIS TS2 targets. Two different and complementary methods were used to measure the residual strain in a tantalum-clad tungsten strip manufactured using the same HIP process as ISIS targets. The strip was produced with deliberately asymmetric cladding, causing it to deflect in proportion to the residual stress. FEA simulations were used to back-calculate the stress from the measured deflection. The strip was then placed on the ISIS instrument ENGIN-X, which allowed detailed through-thickness strain profiles to be measured via neutron diffraction. The results of both methods confirm the presence of large residual strains, and agree reasonably well with FEA simulations of the cladding process.

Nuclear Pressure Vessel Manufacture Using the Hot Isostatic Pressing (HIP) Process

Hot Isostatic Pressing (HIPing) has been used by Rolls-Royce to successfully manufacture nuclear plant components such as valves, piping, and pump casings; the majority of these components being manufactured from stainless steels, typically 316L. There are also considered to be potentially significant benefits to be gained by manufacturing large nuclear plant pressure vessels via the HIP process, such vessels commonly being manufactured from Low Alloy Steel (LAS) materials such as ASME SA-508. The benefits would include cost and lead-time reductions, which are particularly pertinent in relation to the competiveness of the power generation market and future nuclear power plant construction. Such vessels are a major cost and are critical path items of the primary plant. Also, material quality improvements and improved inspectability are possible via the HIP process. Welding vessel sections together using Thick-Section Electron Beam Welding (TSEBW) shows significant promise in reducing welding time and the provision of high quality welds, further reducing vessel cost and lead-time. There is also the potential with the use of TSEBW, to reduce weld inspection requirements with the weld being effectively the same as the parent material, i.e. no weld filler material is used. This paper presents an overview of the pioneering work conducted and planned by Rolls-Royce to develop a method of manufacture to combine HIPing and TSEBW to produce nuclear plant pressure vessels. Staged development is covered, starting with small billet manufacture for the purposes of material testing and examination, followed by vessel demonstrators for the purposes of proving the method of manufacture and to provide justification data, e.g. examination, pressure and thermal cyclic test data. In order to provide a balanced perspective, the paper also identifies the key challenges — risks, and capability development requirements necessary to deliver this method of manufacture.