Effect of Hydrogen Sintering on Phase, Mechanical Property and High Temperature Response of Nanostructured W-60 at. % Cr Defense Alloy

Abstract

Nanostructured W40Cr60 alloy was produced by mechanical alloying (MA) of elemental tungsten (W), chromium (Cr) powder in a high energy ball-mill followed by compaction at 250 MPa pressure and hydrogen sintering at 1500C for 5 h. The evolution of phase and microstructure of the milled powder and consolidated alloy was investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The crystallite size of W in W40Cr60 powder reduced from 100 µm at 0 h to 29 nm at 20 h of milling and lattice strain increases to 0.51% at 20 h of milling. The lattice parameter of tungsten shows initial expansion of lattice upto 0.22% at 5 h of milling and contraction of lattice upto 0.25% at 20 h of milling. The TEM observation revealed that the observed crystallite size (~20 nm) agrees well the measured crystallite size from XRD. Maximum solid solubility of 5.4 at. % Cr in W has been achieved at 20 h of milling. Hardness and Elastic Modulus of sintered W40Cr60 alloy are less compared to pure tungsten. Maximum wear depth and compressive strength of 54.33𝜇m and 914 MPa respectively is achieved in sintered W40Cr60 alloy. Oxidation behavior of the sintered W40Cr60 alloy is also studied at 800°C for 15 h. Comparative study on the oxidation resistance of W, W70Cr30 and W40Cr60 alloy has been carried out to understand the high temperature behavior of pure W and W-Cr alloy. The research work shows encouraging results in terms of enhanced hardness and oxidation resistance as compared to recent study on nanostructured W-Cr alloys.