m. samiee

In this research, the effect of cooling rate on the microstructure, hardness and impact energy of a plastic injection mold made of X210Cr12 steel wasinvestigated. The microstructural studies showed that with increasing cooling rate, the amount of residual austenite (Ar) decreases until it is completely removed.Statistical analysis showed that the size and volume fraction of chromium stabilized with block carbides decreases with increasing cooling rate. As the cooling rate increased, bainites were observed in the microstructure. The hardness decreased via increasing the cooling rate and austenitization time due to the reduced interaction of carbides with dislocations. Martensitic structure prevented a significant reduction in hardness. These factors increased the toughness of the X210Cr12 and led to the ductile failure. Cryogenic treatment modified the structure via distribution of fine carbides into the stable lath martensite. With optimizing the hardness and toughness to withstand the impact of the die, toughness increased to 125 j and hardness decreased to 624 H.V.

In this research, a thin film of TiO2 was applied on AZ91D using the method of magnetic sputtering. Microstructure investigations were conducted using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). Wear resistance for the coating was investigated using the pin on the disk in the form of dry and in the Ringer's solution. the worn surface of the samples was investigated using scanning electron microscopy (SEM) asfter this test. Meanwhile, the level of hardness and flatness of the surface after coating was investigated using Vickers microhardness tester and roughness tester. Results indicated that the coating was formed uniformly and had the globular morphology and very good coherence with the thickness of 90nm, which is seemingly formed at the interface of the coating and substrate of the MgTi2O5 and Mg2TiO4 spinels. The roughness of the surface decreased as much as 20% by applying the coating. Applying the coating decreased the coefficient of friction and increased wear resistance in both of the environments. Following the application a thin film of TiO2, wear mechanism was transferred from severe abrasive to mild abrasive in the dry environment and cleavage crater in the Ringer's solution.