Amir Pakdel; Masoud Emami; Hassan Farhangi; Mohammad Habibi Parsa
Abstract
Al-SiC composites are among the most demanding metal matrix composites due to their excellent strength, good ductility, good corrosion resistance, low coefficient of thermal expansion and reasonable price. Manufacturing of cast metal matrix composites usually involves some problems such as inhomogeneous ...
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Al-SiC composites are among the most demanding metal matrix composites due to their excellent strength, good ductility, good corrosion resistance, low coefficient of thermal expansion and reasonable price. Manufacturing of cast metal matrix composites usually involves some problems such as inhomogeneous distribution of the particles due to poor wetability of ceramics to molten alloys, porosity and formation of particle-void clusters. Thus it seems necessary to utilize secondary processes for these materials in order to obtain suitable properties. In this research Al6061 composites reinforced with 10 volume percent SiC particles of 48?m average size were produced by the stir casting method and effect of extrusion process on the microstructure and strength of these materials was investigated. Results showed that the average particle size and porosity of the composite samples decreased after extrusion. Moreover, tensile strength of the composite increased by increasing the extrusion temperature and/or the extrusion ratio since the pores in the microstructure diminished and the interface bonding was improved.
Ali Ammari Allahyari; Hassan Farhangi; Seyyed Mohammad Mehdi Hadavi
Abstract
The effects of isothermal aging at temperatures between 550-850 ?C for durations of 1-100 h on microstructure, tensile properties, and impact fracture behavior of 316L austenitic stainless steel weld metal have been investigated. For this purpose, various techniques including metallographic observations, ...
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The effects of isothermal aging at temperatures between 550-850 ?C for durations of 1-100 h on microstructure, tensile properties, and impact fracture behavior of 316L austenitic stainless steel weld metal have been investigated. For this purpose, various techniques including metallographic observations, measurement of ferrite content using ferritscope, and fractographic investigations have been utilized. It was found that increasing aging temperature and time lead to dissolution of delta ferrite and formation of a continuous network of sigma phase, followed by partial spherodization of sigma phase. These microstructural changes are found to induce a transition from ductile to brittle fracture mode which is accompanied by a sharp decrease in fracture strain and charpy impact energy, of up to 90%, and is characterized by specific types of fragmented and brittle microvoid fracture surface morphologies. The consequences of such behavior in regards to the selection of proper stress relief heat treatment temperature are discussed based on dividing the aging processing window into three distinct regions.
