Papers by Keyword: Vacuum Arc Melting

Abstract: Permanent biomedical implants pose several issues in long term scenarios like infections, inflammation, implant fracture, tissue damage, cancerous tumors formation, and skin allergies. Biodegradable biomedical implants are a new interest that function by degrading internally after achieving the implant goal. Shape memory alloys like Nitinol and Iron based shape memory alloys have applications in biomaterials due to the excellent property of super elasticity and shape memory effect respectively with the ease of small surgery requirement. To achieve biodegradability, the alloy composition is to be set while not compromising other properties such as biocompatibility, mechanical properties, shape memory properties, and magnetic properties. Slow corrosion rates of Fe-Mn alloys are reported and alloying addition, surface modifications, and novel manufacturing techniques are suggested to overcome this problem. In this study, the effect of addition of copper addition effect on the degradation behavior of Fe-30Mn-5Si is investigated. Austenite is the major phase present in both samples and small amounts of martensite are also present. For 10% copper, an additional copper rich phase is formed along the grain boundaries as it was beyond the solubility limit of iron matrix. The electrochemical corrosion test shows that 10% Cu addition resulted in 1.72 times higher corrosion rate than that of 5% Cu addition. As 5% Cu addition is within the solubility limit of iron matrix, and it forms a solid solution with iron that creates a passive layer during corrosion testing results in slower degradation.

Abstract: Copper matrix composites (CMCs) are widely used in electrical equipment and electrical contact materials due to their excellent electrical properties. Al₂O₃ powders are widely used as a reinforcing agent to enhance mechanical properties of MMCs. The xAl₂O₃/Cu (x =0, 0.2, 0.5, 0.7, and 1.0wt. %) composites were prepared via vacuum arc melting method. The mechanical and electrical properties were obtained by measuring the hardness and conductivity. The morphology of copper and Al₂O₃/Cu composites was characterized by optical microscopy (OM) and scanning electron microscopy (SEM). With the addition of Al₂O₃ from 0.2 wt. % to 1.0 wt. %, the relative densities of composites decreased from 98.5% to 97.0%. The hardness of the composites increased with increase in the Al₂O₃ powders content. The hardness of 1.0Al₂O₃/Cu composites was 57.9 HB, which was higher than that of pure Cu by 18.6%.. With the addition of Al₂O₃, the IACS% of Al₂O₃/Cu composites decreased from 88.97 to 86.16.

Abstract: Three different Fe-C alloys were prepared in vacuum using the arc melting method: hypereutectoid (1.4% C), eutectoid (0.76% C) and hypoeutectoid (0.4% C). Unlike commercial steels, which they always contain Mn and other impurities, our samples were prepared by using high quality powders (99.999 wt.%). The samples were heat-treated and then observed with optical and scanning electronic microscopy (Zeiss EVO MA10). Selected samples were tested by microidentation (microhardness test). After isothermal transformation at 350 °C fine bainite nanostructures were observed in the hypoeutectoid sample, the mean size of which was found to be 50 nm. With the eutectoid sample, following different heat treatment procedures different micro-and nanostructures were measured: pearlite lamellar spacing, spheroidized cementite particles, and martensite needles, whose mean size is 145 nm, 290 nm and 200 nm respectively. The nanostructure of hypereutectoid sample after isothermal transformation at 650 °C, reveals the eutectoid and proeutectoid cementite lamellas with a mean spacing of 390 nm. X-ray diffraction pattern of eutectoid sample indicated the existence of cementite (Fe₃C) content which is also confirmed by carbon mapping of pearlite colonies performed with Energy Dispersive X-ray Spectroscopy. The Vickers hardness of the samples compares well to the one of corresponding commercial steels.

Abstract: Co-based high temperature alloys have been widely used in aeronautics and astronautics industry, because of its high strength at high temperature, excellent resistance of hot corrosion and oxidation. Unlike the traditional Co-based superalloys, strengthened by solution and carbide strengthening, the novel Co-Al-W superalloys are strengthened by a ternary compound with the Ll₂ structure γ-Co₃(Al,W). And the novel Co-Al-W superalloys showing high-temperature strength greater than those of conventional nickel-base superalloys, will become the candidates for next-generation high-temperature materials. We research alloying element Ta effect on microstructure of Co-Al-W superalloys by vacuum arc melting. Compare with the microstructure before and after adding alloying element Ta of Co-Al-W superalloy, we find that most of Ta element distributed in the γ-Co substrate phase, stabilizing and reinforcement the γ phase.

Abstract: Co-Al-W supperalloy used pure element powder, according to the ratio of different atomic percentage composition to make ingredients. It is mixed by planetary ball mill, pressed into blocks after the melting shape. Vacuum arc melting process was prepared by melting, after grinding, polishing, and after a volume of 5% perchloric acid and 95% of the electrolytic etcheing solution prepared in ethanol corrosion observed after analysis of the microstructure and phase composition by XRD analysis .It can be found that Co-Al-W superalloys were mainly composed of cobalt-rich matrix of austenite precipitation of γ phase and coherent with matrix of the L12 structure of γ′-Co₃(Al,W) phase. In addition, Nb have effect on grain refinement and refine grain. Rockwell hardness test and analysis, It can be found that Nb can clearly improve the Co-Al-W superalloy hardness.

Abstract: Shrinkage cavity/piping at the end of the solidified ingot of steels is one of the most common casting problem in 316L austenitic stainless steel ingot, when consumable electrode is melted and cast in a water-cooled copper mould by vacuum arc re-melting furnace. In present study an effort has been made to reduce the size of shrinkage cavity/ piping by establishing the optimum value of hot topping process parameters at the end of the melting process. It is concluded that the shrinkage cavity/piping at the top of the solidified ingot can be reduced to minimum by adjusting the process parameters particularly the melting current density.

Abstract: High temperature structural materials, such as nickel-based superalloys, have contributed immensely to societal benefit. These materials provide the backbone for many applications within key industries that include chemical and metallurgical processing, oil and gas extraction and refining, energy generation, and aerospace propulsion. Within this broad application space, the best known challenges tackled by these materials have arisen from the demand for large, efficient land-based power turbines and light-weight, highly durable aeronautical jet engines. So impressive has the success of these materials been that some have described the last half of the 20th century as the Superalloy Age. Many challenges, technical and otherwise, were overcome to achieve successful applications. This paper highlights some of the key developments in nickel superalloy technology, principally from the perspective of aeronautical applications. In the past, it was not unusual for development programs to stretch out 10 to 20 years as the materials technology was developed, followed by the development of engineering practice, and lengthy production scaleup. And many developments fell by the wayside. Today, there continue to be many demands for improved high temperature materials. New classes of materials, such as intermetallics and ceramic materials, are challenging superalloys for key applications, given the conventional wisdom that superalloys are reaching their natural entitlement level. Therefore, multiple driving forces are converging that motivate improvements in the superalloy development process. This paper concludes with a description of a new development paradigm that emphasizes creativity, development speed, and customer value that can provide superalloys that meet new needs.