Optimization of process parameters and mechanism of strengthening and toughening of Nb-W alloy prepared by chemical vapor deposition based on orthogonal test

Abstract

In this paper, the chemical vapor deposition (CVD) method was used to prepare Nb-W binary alloys on Mo substrates for the first time. The influences of the process parameters on the composition, average deposition rate, and average deposition efficiency of the Nb-W alloys were studied by orthogonal experiments. Nb-W alloys with W contents ranging from 0.33% to 50.48% were successfully prepared. The mechanical properties and fracture morphologies of the Nb-W alloys prepared by the CVD method (CVDNb-W alloys) were tested by metallographic microscopy, scanning electron microscopy, electron probe analysis, and in situ tensile tests. The results showed that the Nb-W alloy prepared by the CVD method had uneven macroscopic distributions of Nb and W.The substrate temperature had the greatest influence on the lateral composition gradient, and the H2 flow had the least influence. The influence of the Cl2 flow through the Nb and W on the average deposition rate was also examined. The chlorination temperature of W had the least effect on the average deposition rate, and the average deposition efficiency decreased with the increase in the gaseous chloride ratio of W. The effects of other factors on the average deposition efficiency showed different degrees of wave dynamics. The metallographic observation of 16 samples showed that except for samples 3# and 4# (in which the mass percentages of W were less than 1%), the microstructures of the other samples (in which the mass percentages of W were all more than 1%) showed similar microstructures with layered structural features. Comprehensive analysis of the sample and inverse pole figures revealed that the (101) textural component mainly existed in the CVDNb-W alloys.With the increase in the mass percentage of W, the tensile strength of the CVDNb-W alloy increased correspondingly. The maximum strength of the alloy containing 9.68% W by mass reached 475 MPa, which exceeds the room-temperature tensile strength of Nb521, but the elongation at break was related to the alloy composition. Thus, the relationship did not show a discernible trend.