• Journal of Powder Materials
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• v.21 no.4
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• pp.294-300
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• 2014

The connecting rod is one of the most important parts in automotive engines, transforming the reciprocal motion of a piston generated by internal combustion into the rotational motion of a crankshaft. Recent advances in high performance automobile engines demand corresponding technological breakthroughs in the materials for engine parts. In the present research, the powder metallurgy (P/M) process was used to replace conventional quenching and/or tempering processes for mass production and ultimately for more cost-efficient manufacturing of high strength connecting rods. The development of P/M alloy powder was undertaken not only to achieve the improvement in mechanical properties, but also to enhance the machinability of the P/M processed connecting rods. Specifically $MoS_2$ powders were added as lubricants to non-normalizing Fe-Cr-Mn-V-C alloy powder to improve the post-sintering machinability. The effects of $MoS_2$ addition on the microstructure, mechanical properties, and machining characteristics were investigated.

• Transactions of Materials Processing
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• v.8 no.3
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• pp.233-233
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• 1999

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62χ)Nb-18Si-l00Mo-l0Ti-χW (χ=0, 5, 10 and 15 mol.%) in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)/sub 5/Si₃, silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti(/sub 5/Si₃, silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.

• Journal of Korea Foundry Society
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• v.13 no.5
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• pp.432-440
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• 1993

Ductile cast iron has a good ductility and toughness than those of gray cast iron, because the shape of graphite is spheroidal. Also, it has been reported that, additional strengthening and toughening of the ductile cast iron can be obtainded from the proper combination of matrix structures by the heat treatment and addition of alloying elements. In this study the effect of special heat treatment and addition of alloying elements(Ni, Mo) on the multi-phase(ferrite-bainite-martensite) structures, strength and toughness of ductile cast iron were studied systematically. In water quenching from $770^{\circ}C$, the martensite volume(%) increased, but the ferrite volume(%) decreased with increment of Ni content. In as cast, pearlite volume(%) and hardness increased with increment of Mo and Ni contents. And with the increment of the destabilization austempering holding time, the bainite volume(%) increased but the martensite volume(%) decreased. As destabilization austempering holding time is same, bainite volume(%) decreased, martensite increased with the increment of Ni and Mo contents. The hardness and tensile strength decreased, but impact energy increased with the decrease of Ni and Mo contents, and increment of holding time of destabilization austempering treatment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.7
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• pp.1132-1137
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• 2003

This study dealt with the suppression of interfacial reaction between Nb and MoSi$_2$ for the fabrication of high toughness Nb/MoSi$_2$ laminate composites, based on the results of a thermodynamical estimation. Especially, the effect of ZrO$_2$ particle on the interfacial reaction of Nb/MoSi$_2$ bonding materials has been examined. Nb/MoSi$_2$ bonding materials have been successfully fabricated by alternatively stacking matrix mixtures and Nb sheets and hot pressing in the graphite mould. The addition of ZrO$_2$ particle to MoSi$_2$ matrix is obviously effective for promoting both the interfacial reaction suppression and the sintered density of Nb/MoSi$_2$ bonding materials, since it is caused by the formation of ZrSiO$_4$ in the MoSi$_2$-ZrO$_2$ matrix mixture. The interfacial shear strength of Nb/MoSi$_2$ bonding materials also decreases with the reduction of interfacial reaction layer associated with the content of ZrO$_2$ particle and the fabrication temperature.

• Journal of Ocean Engineering and Technology
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• v.16 no.6
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• pp.60-64
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• 2002

This paper describes the machining characteristics of the MoSi$_2$--based composites through the process of electric discharge drilling with various tubular electrodes. In addition to hardness characteristics, microstructures of Nb/MoSi$_2$laminate composites were evaluated from the variation of fabricating conditions, such as preparation temperature, applied pressure, and pressure holding time. MoSi$_2$-based composites have been developed in new materials for jet engines of supersonic-speed airplanes and gas turbines for high-temperature generators. These high performance engines may require new hard materials with high strength and high temperature-resistance. Also, with the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material. The tool electrode is almost -unloaded, because there is n direct contact between the tool electrode and the work piece. By combining a non-conducting ceramic with more conducting ceramic, it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and MoSi$_2$ powder was an excellent strategy to improve hardness characteristics of monolithic MoSi$_2$. However, interfacial reaction products, like (Nb, Mo)SiO$_2$and Nb$_2$Si$_3$formed at the interface of Nb/MoSi$_2$, and increased with fabricating temperature. MoSi$_2$composites, with which a hole drilling was not possible through the conventional machining process, enhanced the capacity of ED-drilling by adding MbSi$_2$, relative to that of SiC or ZrO$_2$reinforcements.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.6
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• pp.412-419
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• 2000

There has been a considerable attention on Invar alloys due to its low thermal expansion property. A low thermal expansion property of Invar alloys, lower than $10^{-6}$ near the room temperature, is attractive for electric transmission lines and precision machine tools. However, the expansion property of Invar alloys is limited below about 520K, and mechanical properties are relatively low to apply to electric transmission line. In order to improve mechanical properties in this alloy, Ti alloying element was added to the $Ni_{38}-Mo_2-Cr_1-Fe$ invar alloy. The microstructure Ti added alloy showed finer than that of the unalloyed one. It was found that the (Mo, Ti), Mo carbide formed by Ti addition obstacled grain growth by pinning effect and supplyed recrystallization sites during heat-treatment. Optimum heat-treatment conditions with Ti addition were also discussed in the modified Invar alloy.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.5
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• pp.219-224
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• 2013

In this study, we investigated effect of Mo addition on mechanical properties of Cu added ADI. Ductile cast iron specimens were austenitized at $900^{\circ}C$ for 150 min and then austempered at $380^{\circ}C$ for the various time periods from 15 min to 480 min. Mo added ADI had a higher volume fraction of retained austenite, and the volume fraction of retained austenite was determined by XRD analysis. As decreasing volume fraction of retained austenite, the elongation was also decreased as expected. But the UTS and yield strength were not decreased.

• Proceedings of the KAIS Fall Conference
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• 2001.05a
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• pp.287-289
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• 2001

The morphology of silica supported MoO$_3$ catalysts, which was prepared by impregnation of ammonium heptamolybdate with various weight loadings up to 35 wt%, was studied using x-ray diffraction. In addition to the orthorhombic phase, the behavior of the rarely studied hexagonal phase was characterized. For high loading catalysts, excess ammonium ions present in the monoclinic and triclinic precursors are capable of occupying interstitial sites of microcrystalline MoO$_3$ during moderate temperature calcinations and in doing so enhance the MoO$_3$-SiO$_2$ interaction. This results in a "well dispersed" morphology at high loadings. Sintering at high temperature is due to loss of ammonium from the oxide framework. Ammonia reimpregnation, which leads back to the well dispersed hexagonal phase, may offer a simple regeneration process for spent Mo containing catalysts.

• Journal of the Korean institute of surface engineering
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• v.30 no.2
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• pp.144-154
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• 1997

Effects of plasma nitriding on the surface charcteristice of stainless steel(SS) were investjgated by utilizing wear tester, micro-hardness tester and potentiostat. The surface and corrosion morphology of plasma nitrided SS were analyzed by utilizing optical microscopy, SEM, XRD and WDX. It was found that plasma nitriding at $550^{\circ}C$, compared with $380^{\circ}C$, prodiced a good wear resistance and hardness as nitriding time increased, whereas Mo addition showd that were resistance and hardness decreased. Intergranular corrosion(IGC) resistance improved significantly in the case of plasma nirtrided SS containing 4.05wt% Mo at $380^{\circ}C$ because that nitrogen and Mo ast syner gidically to form a protective layer on surface which is responsible for the aggresive SCN-ion. Plasma nitrided at $550^{\circ}C$ decreased IGC as Mo content increased. Pitting improved in the plasma nitirided SS at Mo content incresased owing to retard a nucleation and growth of chromium carbide or nitirde in grain boundary.

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.469-476
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• 1995

The effects of Cr, Mo or B additions were investigated on $B2{\leftrightarrow}DO_3$ structural transition temperature $(T_C)$ and mechanical properties of Fe-28at.%Al. The raw materials were arc-melted in vacuum and then subjected to the following heat-treatments to maximize the $DO_3$ ordered structure : $1000^{\circ}C/7days$, slowly cooled to $500^{\circ}C$ and then held for 5 days. In the effect on the grain refinment, the addition of alloying element B was the most effective. The addition of Cr or Mo had little effect. When 1at.%Mo was added, $T_c$ increase about $30^{\circ}C$, but Cr had a very little effect on $T_c$. On the contrary, when B was added, $T_c$ was apt to come down minutely. In the additional effect of alloying element on the mechanical properties, Cr was apt to decrease the microvickers hardness and yield strength, Mo and B didn't have much effect. In the case of compressure strength test, the effect of the environment on the yield strength was contrary to the result of the tensile strength test.