A. Patra

Fabrication and Characterization of Novel W80Ni10Nb10alloy Produced By Mechanical Alloying

Nanostructured tungsten (W) based alloy with nominal composition of W80Ni10Nb10 (in wt. %) was synthesized by mechanical alloying of elemental powders of tungsten (W), nickel (Ni), niobium (Nb) in a high energy planetary ball-mill for 20 h using chrome steel as grinding media and toluene as process control agent followed by compaction at 500 MPa pressure for 5 mins and sintering at 1500°C for 2 h in Ar atmosphere. The phase evolution and the microstructure of the milled powder and consolidated product were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The crystallite size of W in W80Ni10Nb10 powder was reduced from 100 μm at 0 h to 45.6 nm at 10 h and 34.1 nm at 20 h of milling whereas lattice strain increases to 35% at 20 h of milling. The dislocation density shows sharp increase up to 5 h of milling and the rate of increase drops beyond 5 to 20 h of milling. The lattice parameter of tungsten in W80Ni10Nb10 expanded upto 0.04% at 10 h of milling and contracted upto 0.02% at 20 h of milling. The SEM micrograph revealed the presence of spherical and elongated particles in W80Ni10Nb10 powders at 20 h of milling. The particle size decreases from 100 μm to 2 μm with an increase in the milling time from 0 to 20 hours. The crystallite size of W in milled W80Ni10Nb10 alloy as evident from bright field TEM image was in well agreement with the measured crystallite size from XRD. Structure of W in 20 h milled W80Ni10Nb10 alloy was identified by indexing of selected area diffraction (SAD) pattern. Formation of NbNi intermetallic was evident from XRD pattern and SEM micrograph of sintered alloy. Maximum sinterability of 90.8% was achieved in 20 h milled sintered alloy. Hardness and wear study was also conducted to investigate the mechanical behaviour of the sintered product. Hardness of W80Ni10Nb10 alloy reduces with increasing load whereas wear rate increases with increasing load. The evaluated hardness value in the present study for all loads is lower than the literature reported hardness of nanostructured W.

Synthesis and Characterization of Oxide Dispersion Strengthened W-based Nanocomposite

The chapter involves fabrication and characterization of novel oxide dispersion strengthened (ODS) tungsten (W)-based nanocomposites used for kinetic energy penetrator (KEP) for defense and plasma facing materials (PCM) for nuclear reactor application. The chapter will discuss the benefits and challenges for using W-based alloys for high-temperature structural application. Synthesis of oxide-dispersed W-based nanocomposite (79W–10Mo–10Ni–1Y2O3) by mechanical alloying followed by consolidation through conventional pressureless sintering and advanced spark plasma sintering is carried out. The phase evolution, microstructure for milled powder, and sintered product have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The densification, hardness, and strengthening behavior of the alloy in two sintering mode are illustrated. The microstructure–mechanical properties are correlated to understand the operative densification and strengthening mechanism. Heterogeneous composition and bimodal grain size distribution of the alloy offers appreciable strength–ductility for structural applications. The chapter will provide a roadmap for design of novel alloys for similar applications.