Effect Of Oxide Dispersion On Microstructure, Mechanical, And High Temperature Behaviour Of Tungsten Based Alloys.

Abstract

Nanostructured tungsten based alloys with nominal composition of W80Ni10Nb10,W79Ni10Nb10(Y2O3)1, W78Ni10Nb10(Y2O3)2, W72Ni10Nb15(Y2O3)3 (all in wt.%) are synthesized by mechanical alloying of elemental powders of tungsten (W), Nickel (Ni), Niobium (Nb) and Yittrium oxide (Y2O3) in high energy planetary ball milling machine followed by compaction at 500 MPa pressure for 5 mins and sintering at 1500o C for 2 h in Argonatmosphere. Investigation of phase and microstructure of milled powder and consolidatedsamples are carried out by X-ray diffraction (XRD), Scanning electron microscopy (SEM),Energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM).Minimum crystallite size of 20 nm is achieved in 20 h milled powder ofW72Ni10Nb15(Y2O3)3.
The dislocation density for all the investigated alloys increases at 10 h of milling owing to hydrostatic pressure exerted by the nano-crystallites due to severe plastic deformation,however the rate of increase of dislocation density reduces after 10 h of milling due to formation of solid solution. The lattice parameter of W in W80Ni10Nb10 and W79Ni10Nb10(Y2O3)1, W78Ni10Nb10(Y2O3)2, W72Ni10Nb15(Y2O3)3 alloy expands at 10 h and 5h of milling and contracts thereafter respectively. The SEM micrograph reveals the presence of ultrafine particles at 20 h of milling for all alloys. Formation of hard, brittle NbNi
intermetallic and Y2O3 disperoids is evident from XRD and SEM study of sintered alloys. Hardness, wear, oxidation, and compression test has been conducted to investigate the mechanical behaviour of oxide dispersion strengthened (ODS) and non-ODS sintered alloys. Increased Y2O3 content results in enhanced compressive strength, sinterability, oxidation resistance and wear resistance. Higher hardness and strength in Y2O3 dispersed alloys as compared to W80Ni10Nb10 can be attributed to dispersion strengthening mechanism by Y2O3.Maximum sinterability, hardness, of 93.38%, 6 GPa, has been achieved in W72Ni10Nb15(Y2O3)3 owing to the presence of high Y2O3 content and NbNi intermetallic.W79Ni10Nb10(Y2O3)1 shows superior oxidation resistance at 8001000°C as compared to restof the alloys.