Porous Titanium Materials Produced Using the HIP Method

Biocompatible porous materials may find use in the manufacture of bone implant components to facilitate bonding of prostheses with bone tissues. The paper presentsa relatively simple method of producing a porous material from the Ti6Al4V alloy by high pressure hot isostatic pressing (HIP). The process was carried out in capsules made of superplastic alloy. The capsules were filled with a mixture of powdered titanium and a carefully selected salt crystals. The mixing ratios had been calculated from the crystal geometry of the components. The experimental verification of the calculation results defined the mixture component ratios, and the processing program was defined, including the temperature and pressure values for the processing stages. Following the HIP process the capsules were opened and the produced material was cleared of salt and examined to determine porosity, size and geometry of voids, and compressive strength.

Heat Assisted Dieless Drawing Process of Superplastic Metal Microtubes - From Zn22Al to β Titanium Alloys

A heat assisted superplastic dieless drawing process that requires no dies or tools is applied to the drawing of a Zn-22Al and β titanium superplastic alloy for not only circular but also noncircular microtubes such as square, rectangular and noncircular multi core tubes having square inner and rectangular outer cross sections. As a result, the tendency has been to increase the limiting reduction in area with increasing strain rate sensitivity index m value. We successfully fabricate Zn-22Al alloy, AZ31 magnesium, β titanium circular microtubes with outer diameter of 191μm, 890μm and 180μm, respectively. Furthermore, a noncircular micro tube, which has inner square tubes with a 335μm side, and an outer rectangular tube of 533×923μm were fabricated successfully. During the dieless drawing process, the geometrical similarity law in cross section which the tube is drawn while maintaining its initial shape can be satisfied. The smooth surface can be obtained in case of superplastic dieless drawing process without contact situation with dies and tools. Consequently, it is found that the superplastic dieless drawing is effective for the fabrication of circular and noncircular multicore microtubes.

Universality of the Phenomenology of Structural Superplasticity

The equation σ=Kέm, where σ is the applied stress, έ is the strain rate, K and m are material constants that depend on stress / strain rate, temperature and grain size is often used to describe structural superplasticity. The general shape of the logσ-logέ curve is sigmoidal. Based on limited data, it was suggested by us earlier that a universal σ-έ curve could exist in a properly normalized space. έ and m are normalized with respect to έopt and mmax, the strain rate at which m is a maximum and the maximum m value respectively. Here a multi-dimensional relationship involving σ/σopt-έ/έopt-m/mmax-ΔF0/kT-η/ηopt is developed; σopt corresponds to έopt, ΔF0 is the free energy of activation for the rate controlling mechanism, k the Boltzmann constant, T the absolute test temperature, η the (apparent) viscosity of the superplastic alloy and ηopt is the viscosity of the same alloy for m=1 in a dimensionless σ-έ space. Using data concerning many systems, the phenomenology of structural superplasticity in all classes of materials is shown to be unique.

Production of a Superplastic Vibration-Damping Steel Sheet Composite Using Friction Stir Forming

This study proposes a novel method of manufacturing composite vibration-damping steel sheet with Zn-22Al superplastic alloy using friction stir forming (FSF). Trials of mechanical interlocking of steel sheet with Zn-22Al superplastic alloy using FSF were carried out on a modified milling machine. The results are discussed in terms of residual microstructures and mechanical properties. We concluded that cladding steel sheet with Zn-22Al superplastic alloy using FSF results in superplastic forming and diffusion bonding.

Effect of Small Addition of Si on Superplastic Elongation at Room Temperature in Zn-Al Eutectoid Superplastic Alloy

Recent experimental data have revealed that a small amount of impurity can significantly influence the superplastic behavior in Zn-Al eutectoid superplastic alloy. However, the effect of Si content on the superplastic behavior in Zn-Al alloy has not been reported. In this study, the superplastic behavior at a room temperature of two grades of the Zn-Al eutectoid superplastic alloy was studied under identical conditions of grain size, temperature, and strain rate. These two grades were prepared from high-purity Zn, Al and Al-Si alloy using the same procedure but different Si impurity levels; Zn-Al-10Si and Zn-Al-1000Si contain 10 and 900 wt. ppm of Si, respectively. As a result of annealing treatments, an average grain size of 0.6 μm in both grades. To investigate the effects of Si content on superplastic properties, the tensile tests were performed at a room temperature of 298 K and a constant strain rate of 1×10-3 s-1. Microstructures before and after the tensile tests was observed using a scanning electron microscope. The experimental results show that the elongations decreased with increasing the Si content. In contrast, the flow stress of Zn-Al alloys was not affected by the Si content. On the microstructure observation of the two grades of the Zn-Al alloy before and after the tensile tests, cavities existed at grain boundaries and strain enhanced grain growth was observed.