No abstract

The effect of austempering temperature on the microstructure of ausferrite in austempered ductile iron was investigated. The results show that the grain sizes of retained austenite and acicular bainitic ferrite both become larger with the increase of austempering temperature. As the austempering temperature is 240°C, the crystallographic relationship between ferrite and austenite in ausferrite follows Greninger-Troiano relation. However, Nishiyama–Wassermann relation and Greninger-Troiano relation both appear in ausferrite austempered at 300°C. At this temperature, the point-to-point misorientations of individual ferrite needle austempered at 300°C are less than 1°, being less than those at 240°C. This means the ferrite needles at 300°C contain fewer defects. However, some poles of ferrite needles obviously deviate from their ideal positions, which mainly comes from some ends of ferrite needles.

No abstract

No abstract

The microstructure of austempered ductile iron was investigated by electron backscatter diffraction technique. The results show that the orientation relationship between acicular bainitic ferrite and austenite is Greninger-Troiano relationship. A single austenite grain is divided into four packets and each packet contains six variants that share a {011} α (i.e., {111} γ) plane. When two γ grains are twinned, the twins share a {111} γ plane and have seven packets. The adjacent acicular bainitic ferrite plates (or laths) sharing a 001 γ axis have small misorientation of about 5.7 •. The adjacent acicular bainitic ferrite plates (or laths) not sharing a 001 γ axis have two high misorientation angles of~54.3 • and~60.0 •. Further, the low angle boundary to high angle boundary ratio is far less than the ratio of the variant pairs with small misorientation to the ones with large misorientation. This work is available for structures obtained as a consequence of the heat treatment of austempering.

Fe-Co duplex coating has been successfully deposited onto pure copper surface by Nd:YAG laser cladding. The morphology and microstructure were investigated by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Mechanical properties of the samples have been evaluated by microhardness measurement and wear properties. Experimental results showed that the coating was free of cracks and voids, and good metallurgical bonded to the substrates. The surface of the Fe-Co duplex coating was mainly composed of α-Co solid solution, CoC x , Fe 0.64 Ni 0.36 and a number of carbides. The microhardness of the Co-based coating reached 438.6 HV 0.2 , which was about 5 times of Cu substrate (90.5 HV 0.2 ). The wear test showed the average wear rate of Fe-Co duplex coating was 19.8% of that of copper matrix. The hardness and wear resistance of the Fe-Co duplex coating was significantly improved.

No abstract

No abstract