Indrani Sen

A Study on Machinability of B-Modified Ti-6Al-4V Alloys by EDM

The effect of microstructural refinement and presence of TiB particles on the electrical discharge machinability of hypoeutectic B-modified Ti-6Al-4V alloys have been studied. This has been characterized on the basis of changes in the following machining responses: material removal rate and tool wear rate. Material removal rate remains unaffected by B addition to Ti-6Al-4V because of insignificant changes in hardness and melting point of the alloy with B modification. On the other hand, microstructural refinement associated with minor amount of B addition leads to enhancement in alloy strength, and hence, tool wear rate has been found to reduce constantly with increasing the amount of B addition. Moreover, the shielding effect of TiB particles, which have higher melting temperature and hardness compared to the Ti-6Al-4V matrix, has also been found to control the wear of the tool.

Microstructure and Mechanical Behavior of a Mini-Thixoformed Tool Steel

We report on mini-thixoforming of a hard and wear-resistant crucible particle metallurgy tool steel. Significant microstructural modifications associated with the special semisolid forming process are characterized in detail by scanning electron microscopy and X-ray diffraction. The mechanical performance of the material is assessed both pre-thixoforming and post-thixoforming by nanoindentation of the constituent phases. The novel microstructural changes that result from mini-thixoforming, which are discussed in this article for the first time, are beneficial in further improving the hardness of the steel.

Mini-thixoforming of a Steel Produced by Powder Metallurgy

Semi-solid processing is complicated by various inherent technical problems. However, once these problems are solved, thixoforming allows intricately shaped components to be manufactured very effectively – often with microstructures that cannot be produced by any other techniques. The recently introduced mini-thixoforming method is an example of such a novel technique for semi-solid processing of steel. The wall thicknesses of resulting parts are about 1 mm. Microstructures of semi-solid-processed steels typically consist of a high proportion of globular particles of metastable austenite embedded in a carbide network, the latter being much harder and more brittle. This paper illustrates that mini-thixoforming allows inverting that microstructural configuration. As an experimental material, powder steel with increased content of vanadium and chromium was used. The post-thixoforming microstructure consisted of a dispersion of carbides and high-vanadium and high-chromium eutectic in an austenitic matrix. Applying optimised processing parameters, complex-shaped parts could be produced. According to the high hardness of resulting microstructural components, the new materials are likely to exhibit extraordinary strength and wear resistance.

Mechanical properties of B-modified Ti-6Al-4V alloys

Minor addition of B to the Ti-6Al-4V alloy reduces the prior beta grain size by more than an order of magnitude. TiB formed in-situ in the process has been noted to decorate the grain boundaries. This microstructural modification influences the mechanical behavior of the Ti-6Al-4V alloy significantly. In this paper, an overview of our current research on tensile properties, fracture toughness as well as notched and un-notched fatigue properties of Ti-6Al-4V-xB with x varying between 0.0 to 0.55 wt.% is presented. A quantitative relationship between the microstructural length scales and the various mechanical properties have been developed. Moreover, the effect of the presence of hard and brittle TiB has also been studied.

Effect of Saline Atmosphere on the Mechanical Properties of Commercial Steel Wire

The effect of saline solution on the mechanical performance of a commercially available galvanized stainless steel wire is studied in detail. Stainless steel of a grade primarily used for automotive applications is used for this study. The investigation is important, especially for considering applications where such wire is subjected to a saline environment. 3.5 pct NaCl solution which replicates seawater composition is used. The quasistatic and fatigue strengths, ductility as well as hardness, and elastic modulus are systematically characterized for the galvanized stainless steel wire pre-immersed in this saline solution. In essence, the role of surface as well as bulk conditions of a material along with the presence of corrosive media in affecting its properties is thoroughly investigated. The results show that pre-immersing the galvanized wire in saline media for a limited time duration of one day produces a protective oxide layer on the surface. This surface layer enhances the resistance of the steel wire against further corrosion. Consequently, the fatigue strength of the material, primarily depending on its surface conditions, improves. On the other hand, the cross-sectional microstructure, protected by the corrosion-resistant outer shell, remains unaffected. The quasistatic strength is also controlled by the bulk of the specimen and therefore varies only nominally. Nanoindentation on the cross-section of the wire reveals no significant changes in the hardness and elastic modulus values as well. This study highlights that optimally pre-immersing in a saline solution improves the fatigue resistance of the galvanized stainless steel wire at the expense of only nominal variations in its tensile properties, hardness, and elastic modulus.