Papers by Keyword: Carbide

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Authors: Vsevolod I. Razumovskiy, Pavel A. Korzhavyi, Andrei V. Ruban
Abstract: Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).
Authors: Yuan Gao, Jin Yong Xu, Yan Ping Liu, Zhi Yong He, Zhong Xu
Abstract: Plasma surface alloying for low alloy high speed power hack saw blades was introduced.The bulk material of the blade is made of low alloy steel, while the teeth of which possess a composition of high speed steel like as a result of surface modification by a plasma surface alloying process.It is a solid diffusion process eliminating method avoids the formation of coarse primary carbides which is a major problem encountered in the production of smelting high speed steel. As a result the carbides in the layer of high speed steel are fine and well-distributed.Therefore,it has not only well wear-resistance but also toughness. Besides, the blade also has the advantages of ease manufacturing and low cost.
Authors: Bei Yue Ma, Ying Li, Jing Kun Yu
Abstract: The latest development of ZrC-SiC, ZrO2-SiC and ZrO2-mullite high performance composites synthesized from zircon was reviewed. The future development of synthesizing high performance composites from cheap materials and simple preparation technology was prospected.
Authors: Yi Kun Luan, Nan Nan Song, Yun Long Bai, Xiu Hong Kang, Dian Zhong Li
Abstract: A novel segregative carbide was discovered during the manufacture of high speed steel roll. The carbide with rectangular shape is a type of MC carbide not yet reported in the open literature. It is a face centered cubic carbide with a lattice parameter a=0.414445 nm, very close to the VC carbide but with a different chemical composition. The M represents the metallic elements (at.%): 91.80 V, 3.17 Cr, 2.19 Fe and 2.83 Mo.
Authors: Jae Kyoung Shin, Soo Woo Nam, Soo Chan Lee
Abstract: To understand the effects of nitrogen on high temperature, creep-rupture tests have been conducted at 973 and 1073K for 18Cr-9Ni austenitic stainless steels with 0.14 and 0.08wt% nitrogen contents. It is observed that creep-rupture life of 18Cr-9Ni-0.14N steel is longer than that of 18Cr-9Ni-0.08N steel. To verify the difference in creep-rupture life between two alloys, scanning electron microscope and transmission electron microscopy are used to observe the microstructure. From the observations, it is known that the Cr-rich carbides are precipitated mainly at the grain boundary. Comparing the ratio of the linear density of the precipitate particles, the higher nitrogen content is, the less carbide is precipitated. Nitrogen might retard the formation of carbides at the grain boundary and reduce the density of cavity sites which are one of the main grain boundary damages.
Authors: Armansyah Ginting, Mohammed Nouari, Nadhir Lebaal
Abstract: In this paper, the surface integrity is studied when machining the aeronautical titanium alloys. Surface roughness, lay, defects, microhardness and microstructure alterations are studied. The result of surface roughness judges that the CVD-coated carbide fails to produce better Ra value than the uncoated. Lay is characterized by cutting speed and feed speed directions. Feed mark, tearing surface, chip layer formation as built up layer (BUL), and deposited microchip are the defects. Microhardness is altered down to 350 microns beneath the machined surface. The first 50 microns is the soft sub-surface caused by thermal softening in ageing process. Microstructure alteration is observed in this sub-surface. Down to 200 microns is the hard sub-surface caused by the cyclic internal work hardening and then it is gradually decreasing to the bulk material hardness. It is concluded that dry machining titanium alloy is possible using uncoated carbide with cutting condition limited to finish or semi-finish for minimizing surface integrity alteration.
Authors: Yi Kun Luan, Nan Nan Song, Xiu Hong Kang, Dian Zhong Li
Abstract: Carbides in HSS roll were studied systematically. The results showed that there were two kinds of carbides in HSS roll, 1st and 2nd carbides. 1st eutectic carbides included the chrysanthemum-like MC mainly consisting of V and the plate-like M2C rich in Mo. 2nd carbides were complex carbides, concentrating Fe, Cr, Mo and V elements. The morphology, distribution and alloy concentration of the 1st eutectic carbides were studied using OM, SEM and EDS. During heat treatment, evolution of the 1st eutectic carbides was analyzed. It was found that the MC carbides had no change in morphology, components and distribution, while the M2C carbides decomposed to M6C and MC. In order to improve the properties of HSS, a method of increasing solidification rate was defined to refine the eutectic carbides. After refinement, the eutectic carbides distributed both along the grain boundaries and inside the grains.
Authors: Hyun Uk Hong, Hi Won Jeong, In Soo Kim, Baig Gyu Choi, Young Soo Yoo, Chang Yong Jo
Abstract: The formation of serrated grain boundaries and its subsequent effect on creep resistance have been investigated in a wrought nickel based superalloy Nimonic 263. The grain boundaries were considerably serrated without the presence of γ' phases or M23C6 when a specimen was slow-cooled from the solution treatment temperature. The high resolution observation on the lattice image of the serrated grain boundary suggested that the grain boundaries tended to serrate to have specific segments approaching to one {111} low-index plane at a boundary in order to have lower interfacial free energy of grain boundary. The grain boundary serration led to a change in M23C6 carbide characteristics: the carbide morphology from granular to planar, a lowered density and their coherency pattern to two neighboring grains from consistent to zigzag. The improvement of creep resistance was noticeably observed by the introduction of GB serration without deterioration of basic mechanical properties. This improvement in creep resistance by the serration was associated with a lower rate of cavitation and crack propagation through the modification of carbide characteristics as well as grain boundary configuration.
Authors: In Gee Kim, Gul Rahman, Jae Hoon Jang, You Young Song, Seung Woo Seo, H.K.D.H. Bhadeshia, A.J. Freeman, G.B. Olson
Abstract: The formation enthalpy of a series of Fe-C carbides has been estimated using a first-principles approach. The Fe to C ratio dependence of the formation enthalpy is reasonable, but it is revealed that - and -carbides require an extraordinary environment to be able to form. Furthermore, an addition of substitutional solutes other than Fe and C should promote other carbides with different crystal structures. The analysis suggests further studies to discover the critical concentrations of alloying which stimulate the other carbides to become more stable.
Authors: Shao Bo Zheng, Yue Gong, Dan Zhao, Qing Lin Lu, Hui Gai Li
Abstract: The effect of magnesium on the morphology and composition of the carbide in annealed bearing steel was studied. The morphology of carbide was observed and statistical analysis was carried out. The results showed that the non-uniform distribution of carbides in bearing steel was obviously improved with increasing the content of magnesium. Segregation thermodynamics indicated that the segregation of magnesium to grain boundaries prevented element such as Cr, C from enriching on grain boundary, which was helpful for the reduction of network carbide precipitation. The chemical analysis results proved this viewpoint.
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