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Authors: Z. Shi, Jia Wei Mi, Patrick S. Grant
Abstract: A numerical finite difference model has been developed to describe the transient heat flow inside Ni superalloy IN718 billets manufactured by spray forming. This model described the progressive build-up and solidification of the billets, and accounted for the latent heat of solidification, convective and radiation heat loss, and heat removal through the substrate, coupled with transient heat transfer in the substrate. The model has been used to predict critical values of important process parameters: average droplet arrival temperature, deposition rate, and billet surface convective heat transfer coefficient, in terms of key microstructural features by correlation of quantitative predictions with qualitative microstructural investigations of the as-sprayed billets. On a micro scale, repeated re-heating/remelting of deposited layers because of subsequent deposition was predicted and has been suggested to be beneficial in reducing porosity and microsegregation, as well as in playing an important role in the formation of the characteristic equiaxed spray formed microstructure.
Authors: Jia Wei Mi, Z. Shi, Patrick S. Grant
Abstract: A finite element model has been developed to simulate the coupled effects of deposit shape evolution and heat flow inside spray formed ring-shaped deposits. The shape model was developed using Matlab and included the features of: (1) atomiser scanning; (2) substrate movement relative to the atomiser; and (3) sticking efficiency. Atomiser scan and various substrate horizontal travel speeds were studied to optimise the ring shape in terms of useful materials suitable for downstream processing. The heat flow model was developed using the commercial finite element code Femlab. A data mapping technique was developed to transfer thermal data between different domains when the computational domains are subject to changing geometry and therefore the coupled effects of shape evolution and heat flow were addressed. Spray forming of ring deposits was performed on the large spray forming unit at Oxford University. In-situ temperature measurements were carried put for acquisition of boundary conditions and validation of the heat flow model. Heat flow modelling revealed that edge effects had a strong influence on the ring thermal history and the porosity distribution inside the deposits is closely related to the local solidification time.
Authors: Ying Dong Qu, Cheng Song Cui, San Ben Chen, Qing Chun Li
Abstract: A PID controller has been developed to improve the dimensional precision of a deposit during spray forming. Simulation has been carried out based on a dynamic neural network modeling of deposit dimension. The simulation results show that the PID controller is effective for the control of deposit dimension with short regulating time and low override. Experimental results show that the error between the actual size and the target value is very small even though a disturbance from unstable melt flow rate was introduced.
Authors: Jun Fei Fan, Yin Zhang, San Bing Ren, You Duo He, Jing Guo Zhang, De Sheng Sun, Hai Rong Le
Abstract: The simulation software of compressible gas flow process in spray forming equipment was developed under three-dimensional cylindrical coordinates. When the gas flow strands sprayed from some definite angles into the atomizer chamber, they converged at the definite height in axial line then expanded outside which showed the jet current characteristic. The substrate stagnated the divergence jet strands of gas and then separated the flow strand into two big recycle zones in whole space. One of the recycle flow zone directed downwards, the other recycle flow zone, directed upwards and reached the inlet area, which is the main reason caused the bonding of small liquid drop in the delivery hole.
Authors: Yin Zhang, Jun Fei Fan, You Duo He, San Bing Ren, Jing Guo Zhang, De Sheng Sun, Hai Rong Le
Abstract: Through the probability simulation method, the statistical model of mass metal liquid droplets during metal spray forming process was developed and the ejecting process of molten steel was studied. The distribution of metal liquid droplets, their different initial velocity and the original appear location during spray forming were obtained based on the above computation. After made statistic and analyzed on large number of metal liquid droplets, the forming and motion of liquid drop in whole space were defined in detail, which provided the precondition and reference for further study of liquid droplets deposition process on substrate.
Authors: Jian Cheng Fang, Wen Ji Xu, Zhi Yu Zhao, L. Wang
Abstract: There are many technical parameters influencing on the coating quality in plasma spray forming which has become an important technology in materials processing. In this study, the relationships between the melting state, in-flight property of particles injected into plasma jet and the forming quality have been investigated. The experimental results show that the temperature field distributions of plasma jet are mainly affected by plasma generator power though CCD imaging and gray-scale processing. The velocity of in-flight particle is directly determined by the flow rate of work gas, and the surface temperature of in-flight particle is obviously affected by assisted gas rate. It is clear that the energy coupling and momentum transferring between plasma and particle have a significant influence on deposition efficiency, porosity, microhardness and microstructure of spray-formed parts, and it also provides a good idea to control the forming quality on-line.
Authors: Won Yong Kim, In Dong Yeo, Tae Yeub Ra, Mok Soon Kim
Abstract: The microstructure and mechanical property of Al 5083 alloy produced by spray forming and then subsequent hot extrusion at 693 K were investigated. In order to compare the mechanical property and microstructure permanent casting and hot extrusion was also carried out in air. The spray formed Al 5083 alloy showed the microstructure consisting of Al matrix phase, MnAl6, FeAl6 and Mg2Al3 dispersoids. This microstructural feature analyzed is quite similar to Al5083 alloy prepared by conventional casting. However, a noticeable difference in grain size appeared between those alloys with different processing. It is found that spray forming plays an effective role to reduce the grain size of the present Al 5083 alloy. At room temperature, the yield strength of spray formed alloy was higher than that of permanent casting alloy. At high temperature, spray forming appeared to display a higher elongation value than conventional casting. It is therefore suggested that spray forming of the present Al 5083 alloy promotes to increase yield strength at room temperature and to increase elongation at high temperature. Details will be discussed in relation with the results obtained.
Authors: Hai Sheng Shi, Jun Fei Fan, Jing Guo Zhang, Hai Rong Le, Yong Peng, Bing Zhong Jin, Xiao-chuan Mi
Abstract: The CuNi15Sn8 alloy has quite potential applications in the field of the electrical appliance industry. However, this alloy is prone to generate the segregation of alloying elements at the grain boundaries because of the high content of Sn element with the low melting point by conventionally processing route. Although the CuNi15Sn8 alloy can be obtained by powder metallurgy or mechanical mixing techniques, it is hard to avoid the formation of oxidation in the alloy. As compared with these techniques, spray forming technique has obvious advantages in preparing the CuNi15Sn8 alloy. The spray formed CuNi15Sn8 alloy has indicated that the elements of Sn and Ni were very uniformly distributed in matrix with the fine equiaxed grains. Influence of aging treatment on the microstructure and properties of spray formed CuNi15Sn8 alloy was studied.
Authors: Meiyan Zhan, Zhen Hua Chen, Hong Ge Yan, Weijun Xia
Abstract: The evolution of SiC particle distribution in spray codeposition SiCp/7075Al composite during extrusion was investigated. A unique metallurgical pattern designated as ring- and band-pattern in the cross section of the extruded products occurred which comprises areas with higher and lower concentrations of SiC particles. The factors that contributed to the evolution of SiC particles distribution feather during plastic deformation were analyzed. The difference of flowability between the matrix and SiC particles was supposed to be the main factor accounting for the forming of the ring- and band-pattern. In addition, concentration difference of SiC particles between different deposition layers will also contribute to the forming of the ring- and band-pattern. A simple model was proposed to describe the evolution of SiC particle distribution during extrusion.
Authors: Xiao Jun Li, Jing Guo Zhang, Hai Sheng Shi, Jian Sheng Wu

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