The effect of semi-solid forming process is better than other methods such as modification. However, the possibility of defects (shrinkage porosity) is increased due to low pouring temperature. Generally, extrusion equipment is required, which is complex and costly.
The defects caused by hot rolling are the same as those caused by other hot rolling technologies. As a brittle phase, carbide can not be filled in time in the gap caused by thermoplastic deformation and fracture, and the micro cracks are easy to lead to stress concentration and internal defects.
In order to develop high temperature erosion resistant materials, noriyuki Hayashi prepared ternary chromium alloys by mechanical alloying and sintering. The results show that the prepared alloy has good microstructure, Vickers hardness is more than 6 GPA, and the erosion wear resistance at 973 K is basically the same as that of Cr3C2 / Ni cermet with high wear resistance.
In situ TiC Reinforced High Chromium Cast Iron (hcwi) composites were prepared by Shibo Li. With the help of the special thermodynamic properties of powder metallurgy, the reinforced phases (TIC, carbide) are uniformly distributed in the matrix. The toughness and wear resistance of the reinforced and modified hcwi composites are 8 times higher than those of the unreinforced hcwi composites. Using alloy powder as raw material, high chromium cast iron alloy is prepared by powder metallurgy method, which can provide unique thermodynamic conditions for microstructure evolution in casting process. Firstly, the atomized powder has a rapidly solidified microstructure; Secondly, the solid or liquid sintering temperature is much lower than the melting or pouring temperature in the casting process, which will inevitably affect the nucleation and growth of carbides, and change the morphology of carbides.
The existing research on the control of carbide morphology, distribution and size in the solidification structure of chromium based alloys is often focused on the addition of modifier and heat treatment after solidification, which is based on the principle of early solidification to improve the structure and morphology of carbide to a certain extent. The new preparation methods of powder metallurgy fundamentally change the solidification process of alloy from the basis of thermodynamics and kinetics, so as to change the structure morphology, rather than just optimize the alloy structure from external factors. The solidification structure obtained in this way can greatly improve the mechanical properties of the alloy. However, chromium based alloys are often used in wear-resistant parts with large size profile, and powder metallurgy method has no advantage in preparing such specimens. In addition, the preparation method of powder metallurgy is more complex than ordinary casting process, and the cost is relatively high, which limits its application in the preparation of chromium alloys.
