Abstract
A numerical model was developed to simulate the jet-flow solid fraction of W18Cr4V high-speed steel during spray forming. The whole model comprises two submodels: one is an individual droplet model, which describes the motion and thermal behaviors of individual droplets on the basis of Newton’s laws of motion and the convection heat transfer mechanism; the other is a droplet distribution model, which is used to calculate the droplet size distribution. After being verified, the model was used to analyze the effects of parameters, including the initial gas velocity, deposition distance, superheat degree, and the ratio of gas-to-metal mass flow rates, on the jet-flow solid fraction. Finally, an equation to predict the jet-flow solid fraction directly and conveniently according to the parameters was presented. The values predicted by the equation show good agreement with those calculated by the numerical model.
Highlights
As a novel rapid solidification and near-net-shape technique, spray forming has various advantages, such as elimination of macrosegregation compared to casting technology and fewer process steps compared to conventional powder metallurgy
FGH95 superalloy [4], AA7050 alloy [5], Al−50Si alloy [6], and Cu−11.85Al−3.2Ni−3Mn shape memory alloy [7] exhibit fine and uniform microstructures as well as good mechanical properties when prepared by spray forming
The jet-flow solid fraction fs is calculated by combining the individual droplets solid fraction and the droplet size distribution
Summary
As a novel rapid solidification and near-net-shape technique, spray forming has various advantages, such as elimination of macrosegregation compared to casting technology and fewer process steps compared to conventional powder metallurgy. During the spray-forming process, the surface solid fraction of the deposited preform is a key factor determining the properties and qualities of the products. Grant et al [8] established an individual droplet model to investigate the motion and thermal history of a droplet Using this model, the influential parameters for spray forming, including the droplet size distribution, initial axial gas velocity, melt mass flow rate, melt superheat, and the alloy. Few simulation studies concerning spray-formed high-speed steel have been reported. The previous simulation results cannot be directly applied to the spray forming of high-speed steels. The motion and heat-transfer mechanisms of W18Cr4V high-speed steel droplets during spray forming were investigated and the optimal production parameters were discussed
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