Papers by Keyword: Thermal Fatigue Resistance

Abstract: In order to enhance surface property of brake materials, compacted graphite cast iron (CGI) with non-smooth surface was processed by laser local processing. This study focuses on the influence of the work media on wear resistance and thermal fatigue resistance of specimens. The results showed that when the work media were air and water respectively, laser local processing could enhance surface property of CGI. Changing work media could not change phase compositions of the laser processing area, but refined their microstructures, which enhanced their micro-hardness. By this way, the specimens’ wear resistance and resistance to thermal crack initiation were further improved, while their resistance to thermal crack propagation was influenced by cracks on bionic units.

Abstract: Silicon nitride nanoceramics were prepared by hot press sintering amorphous Si₃N₄ and α-Si₃N₄ nanopowders. The microstructures as well as the effect of starting powders size on the mechanical properties and thermal fatigue properties were investigated. The results show that microstructure of sintered materials consists of spherical grains with approximate size of 100 nm. The mechanical properties and thermal fatigue resistance vary with the addition of α–Si₃N₄ powders. The maximum flexural strength and fracture toughness are obtained when the α–Si₃N₄ powders amount is 40wt.%. And the Si₃N₄ nanoceramic added 40wt.% α–Si₃N₄ powders has the best capability to suppress crack propagation and the highest critical temperature difference.

Abstract: This paper focuses on the influence of processing methods on the cracks’ number and form of bionic units on the vermicular cast iron. The results show that there have already been cracks on the bionic units’ surface, and the crack number increases with the thermal cycles. The crack’s form on bionic units processed in air is tree-like structure, and that of bionic units processed in water is network structure. The twice laser process and the electro-pulsing treatment can effectively reduce the crack number of the bionic units processed in water, without changing the form.

Abstract: To meet the high requirements of fatigue strength and thermal stability for the large forging dies, the complex strengthening process tests of new high thermal stability die steel 5Cr2NiMoVSi were done. This complex strengthening process was nickel plating the RE boron penetration→ pre-cool quenching → high temperature tempering. The results show that the surface micro-hardness, high temperature oxidation resistance, thermal fatigue resistance and wear resistance of 5Cr2NiMoVSi steel can greatly be improved by these processes. It has achieved significant results for auto front axle large forging dies by using the materials and processing technology.

Abstract: The microstructure and properties of ternary boride ceramic coating prepared by reactive flame spraying on surface of H13 steel are studied as well as the microstructures, microhardness, wear resistance and thermal fatigue resistance of the coating. The results show that the Mo2FeB2 cermet coating by reactive flame spraying has good wear resistance and thermal fatigue resistance and its microhardness can even reach 1200 HV.

Abstract: The surface composite layer Ni/WC on the cast iron substrate was fabricated through vacuum infiltration casting technique using Ni-based powder and WC particles with different content as raw materials. The micro-structure of infiltrated layer was compact for all infiltrated layer with different WC content, and WC particles distributed uniformly. The surface infiltrated layer was mainly composed of WC particle, intermetallic compound and solid solution. The thermal cycles were beyond 108 times when the infiltrated layer peeled off, which indicated that the specimen with infiltrated layer offered excellent thermal fatigue property. The oxidation rate of substrate was nearly three times as large as that of the infiltrated layer with 20% WC content. The oxidation resistance of the infiltrated layer improved obviously comparing with the substrate because the oxide layer for infiltrated layer was compact.

Abstract: The influence of rare earths(RE) and Mg compound modification on eutectic carbide morphology and matrix of high speed steel(HSS) roll was investigated. The results show that the matrix can be refined by the RE-Mg compound modifier, the eutectic carbides are inclined to turn into small lump, whose distribution is homogeneous. After modification, the heat conductivity coefficient of HSS is increased and heat expansion coefficient is decreased. Moreover, RE-Mg modification is able to increase the cycles of thermal fatigue crack initiation and decrease the propagation rate. After cycling 700 times at the condition of heating at 600oC and cooling in 25oC water, the length of thermal fatigue crack is lessened by 41.12%.