Academic literature on the topic 'Sprayforming'

Three kinds of master alloys, including scrap material, vacuum induction melting (VIM) ingot and electro slag remelting (ESR) ingot, were spray formed into different billets. The influence of master alloy on the cleanliness of spray formed superalloy was investigated by means of electron beam (EB) button melting and Scanning Electron Microscopy (SEM), on the basis of optimized process of spray forming and EB button melting. The results show that the inclusions in spray formed preform are mainly composed of alumina and magnesia, stem from master alloy and some refractory materials in the process of remelting. The cleaner the master alloy, the lower level of inclusion contents of the billet. Among three kinds of master alloys, the ESR ingot exhibit the cleanest melt surface in the process of re-melting and contains much smaller inclusions in EB button. The cleanliness of spray formed billet is better than ingot stack for deposition. Superclean sprayforming billet with smaller size inclusions (<100μm) can be attained by the ESR ingots.

碩士<br>國立成功大學<br>材料科學及工程學系碩博士班<br>91<br>The study aims at, on one hand, the effect of process parameters on micro-structural evolution of low content silicon aluminum alloy when taking advantage of Sprayforming techniques which is compared with casting. And, on the other hand, the characteristics of mechanical behavior and bulk workability of as-sprayformed AlSi billet need estimated. Compared with conventional casting processes, as-sprayformed billet shows refined microstructure and macro-segregation elimination. 　　The experimental results show that the grain size of as-sprayformed billet is about 40~50 μm. At center and middle position of the billet, it shows equaxed structure. The porosity of as-sprayformed billet can be reduced by lowering the gas-to-metal-flow ratio from 3.7 level down to 1.7 level. The micro-structure of AlSi of the same composition by casting is dendrite. After being hot pressed, both of the as-sprayformed and as-cast samples show two typical common characteristics: undeformed zone and shearing zone. Undeformed zone in as-sprayformed samples show equaxed microstructure and that in the as-cast one shows dendrite. The shearing zone in the as-sprayformed samples show elongated grain. Since difference orientation exists between the shearing direction and the second dendrite arm, the dendrite shows either elongated or bended in as-cast samples. 　　The uniaxial compressing tests are carried out for as-sprayformed and as-cast samples. The experimental results indicate that yield strength decreases when the temperature is increased. Both samples are aluminum matrix and the crystal structure in FCC. In FCC structures, there two controllable mechanisms when yielding. One is based on material characteristic and the other is thermal activated. On increasing temperature, the thermal activated mechanism becomes more important, resulting in decrease of yield strength for both. When increasing cross head speed, the yield strength increases. Higher initial strain rate results in shorter response time for the production of dislocation. In the same time interval, higher initial strain rate produces higher density of dislocation. Difference yield strength is owing to the different micro-structure. 　　There exists a plateau deformation zone for both. The plateau deformation zone for as-sprayformed is more extended, indicating that the as-sprayformed sample is capable of being deformed more. There is serration in flow stress owing to the dynamic strain ageing (DSA) Dynamic strain ageing cause the flow stress curve zigzag-like when the cross head speed is 3 mm/sec and the temperature is ranging from 325℃ to 425℃。When deformed to high strain, the flow stress of as-cast samples increase. The experimental results indicate as-cast sample is deformed more inhomogeneous. 　　Finite Fourier Transformation of roughness indicates that the response wavelength of the as-sprayformed billet is even smaller than that of the as-cast ones. Different response wavelength produces different morphology for the as-sprayformed and as-cast samples after uniaxial compressing.