Conventional Induction Melting Research Articles

Synthesis of Nb0.8Hf0.2FeSb0.98Sn0.02 and Hf0.25Zr0.25Ti0.5NiSn0.98Sb0.02 Half-Heusler Materials and Fabrication of Thermoelectric Generators

In this study, half-Heusler (HH) thermoelectric materials Nb0.8Hf0.2FeSb0.98Sn0.02 (p-type) and Hf0.25Zr0.25Ti0.5NiSn0.98Sb0.02 (n-type) were synthesized using induction melting and spark plasma sintering. For alloying, a conventional induction melting technique was employed rather than arc melting, for mass production compatibility, and the thermoelectric properties of the materials were analyzed. The maximum dimensionless figures of merit (zTmax) were 0.75 and 0.82 for the p- and n-type material at 650 oC and 600 oC, respectively. These materials were then used to fabricate generator modules, wherein two pairs of p- and nlegs without interfacial metal layers were brazed on direct bonded copper (DBC)/Al2O3 substrates using a Zrbased alloy. A maximum power of 0.57 W was obtained from the module by applying a temperature gradient of 476 oC, which corresponds to a maximum power density of 1.58 W cm -2 when normalized by the area of the material. The maximum electrical conversion efficiency of the module was 3.22% at 476 oC temperature gradient. This value was negatively affected by the non-negligible contact resistivity of the brazed interfaces, which ranged from 6.63 × 10 -9 Ωm2 to 7.54 × 10 -9 Ω m2 at hot-side temperatures of 190 oC and 517 oC, respectively. The low electrical resistivity of the HH materials makes it especially important to develop a brazing technique for ultralow resistance contacts.

Characteristics of electrochemical hydrogen storage using Ti–Fe based alloys prepared by ball milling

In this paper, the TiFe-based master alloy Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 was fabricated by conventional induction melting with high purity helium as the protective gas. After that, the as-cast specimens were mechanically milled with nickel powders to synthesize the as-milled Ti1.04Fe0.7Ni0.1Zr0.1Mn0.1Pr0.06 + 10 wt.% Ni composites with excellent electrochemical characteristics. The master alloy is composed of TiFe, Ti2Fe and Pr phases, which has a typical crystal structure. Mechanically milling the master alloy with nickel powder leads to the reductions of the grain size and particle size, even forming amorphous structure. The experimental results showed that the specimens after ball-milling treatment can be used to hydriding and dehydriding by electrochemistry, getting the maximal discharge capacity in the first cycle, and no activation was required. The discharge capacity of the as-milled composites declined from 264.2 to 133.6 mAh/g with the milling duration extending from 5 to 30 h. The electrochemical kinetics markedly declined with prolonging milling duration. However, the electrochemical cycling stability of the specimens reduced firstly and then increased with the prolongation of grinding duration.

Effect of arc re-melting on microstructure, mechanical and tribological properties of commercial 390A alloy

To investigate the effect of the arc re-melting on the microstructure, mechanical and tribological properties of the 390A alloy, its ingot produced by the conventional induction melting method was subjected to the arc re-melting process. The microstructure of the 390A alloy was examined by OM and SEM. Mechanical properties of the 390A alloy were determined by the Brinell method and tensile tests. Tribological properties were investigated with a ball-on-disc type tester. It was observed that the microstructure of both conventional induction melted and arc re-melted 390A alloys consisted of α(Al), eutectic Al–12Si, primary silicon particles, θ-CuAl2, β-Al5FeSi, δ-Al4FeSi2, and α-Al15(FeMnCu)3Si2 phases. Re-melting with the arc process caused grain refinement in these phases. In addition, after this process, the α(Al) phase and primary silicon particles were dispersed more uniformly, and sharp edges of primary silicon particles became round. The arc re-melting process resulted in an increase in the hardness of the 390A alloy produced by the conventional method from 102 HB to 118 HB and the tensile strength from 130 to 240 MPa. It also caused an increase in the wear resistance of the 390A alloy and a decrease in the friction coefficient.

Compression stress strengthening modelling of a ultrafine-grained equiatomic SPS CoCrFeNiNb high-entropy alloy

High-entropy alloys are known to show exceptionally high mechanical properties, both compression and tensile strength, and unique physical properties, such as their phase stability. These quite unusual properties are primarily due to the microstructure generated by mechanical alloying processes, such as conventional induction arc melting, powder metallurgy, or mechanical alloying. In the present study, an equiatomic CoCrFeNiNb high-entropy alloy was prepared by a sequence of conventional induction melting, powder metallurgy, and compaction via spark plasma sintering. The high-entropy alloys showed uniform sub-micrometer grain microstructure consisted by a mixture of an fcc solid solution strengthened by a hcp Laves phase and a third intergranular oxide phase. The as-cast high-entropy alloys showed an ultimate compression strength (UCS) of ∼1400 MPa, which after sintering and compaction at 1273 K increased up to ∼2400 MPa. Extensive transmission electron microscopy quantitative analyses were carried out to model the UCS. A quite good agreement between the microstructure-strengthening model and the experimental UCS was found.

High-strength ultrafine-grained CoCrFeNiNb high-entropy alloy prepared by mechanical alloying: Properties and strengthening mechanism

Abstract An equiatomic CoCrFeNiNb alloy was prepared by conventional induction melting and by 8 h of mechanical alloying and compaction via spark plasma sintering. The alloy prepared via mechanical alloying showed a uniform ultrafine-grained microstructure composed of an FCC solid solution strengthened by HCP Laves phases. A detailed TEM inspection revealed the presence of nanocrystalline Cr2O3 particles at the triple junctions of the present grains as well as stacking faults and nanotwins found exclusively in the interior of the FCC solid solution grains. The as-cast alloy had a high initial hardness of 648 ± 18 HV 30 and ultimate compressive strength of 1374 MPa. On the other hand, the mechanically alloyed alloy compacted at 1000 °C showed even higher hardness of 798 ± 9 HV 30 as well as an ultra-high strengths that reached 2412 MPa. Based on the TEM quantitative analyses considering the contributions of different structural constituents and lattice defects, the aforementioned strength value was found to be in good agreement with results from microstructure strengthening modelling, which indicated a calculated mean value of 2300 ± 300 MPa. Moreover, the mechanically alloyed alloy also showed exceptional thermal stability even after long-term annealing/testing at 600 °C because it maintained a hardness of 777 ± 5 HV 30, and strength of 2284 MPa.

The Effect of Electromagnetic Stirring on the Microstructure Evolution of Cu-15%Co Alloy

Cu-15%Co alloys have been synthesized by an induction furnace adopting electromagnetic stirring (EMS). The liquid-liquid separation behavior and the peritectic reaction under a forced melt flow were analyzed. The specimens were subjected to a conventional induction melting as well as enhanced melt stirring by a two-side electromagnetic stirrer. The stirred ingots showed a significant improvement in dispersivity and homogeneity of the Co-rich phase. Comparing the specimens subjected to different current intensities, we observed strong changes in the phase fraction, the degree of segregation, and the grain size. EMS had an effect of reducing the amount and size of Co-rich droplets and enhancing the amounts of small equiaxed dendrites and dendrite fragments, which led to a more dispersive distribution of α-Co phase and refined the grains of Cu-rich phase. We observed a considerable increase in the fraction of peritectic Cu-rich phase with increasing current intensity of EMS, indicating that the peritectic reaction was promoted by EMS. EMS also reduced the macrosegregation of Co-rich phase in both the vertical and radial direction of the ingot when the current intensity was appropriate.

Tensile, Impact, Wear and Corrosion Behavior on Conventionally Melted Nitrogen Alloyed Martensitic Stainless Steel in hot forged, hardened and tempered conditions

In the recent years, the need for corrosive resistive high strength materials with less cost has become a mandatory requirement for several applications. Though there are many advanced materials available with better properties still the researchers are in search of a material with high corrosive and wear resistance property. Therefore, the main aim of the present investigation is to develop high strength Nitrogen Alloyed Martensitic Stainless Steel (NAMSS) by conventional induction melting. Six different combinations of the NAMSS were prepared to understand the effect of nitrogen alloy on martensitic stainless steel in hot forged, hardened and tempered conditions. So far, tensile, impact, wear and corrosion tests were carried out in the NAMSS and it was found that the tensile strength are being increased when addition of nitrogen alloy but the impact toughness, wear and corrosion properties are also increased up to a certain level of nitrogen but they are subsequently decreasing on further addition of nitrogen. The fracture morphology were revealed by SEM and it shows ductile and quasi-cleavage fracture on the surfaces.

Rapid preparation of InxCo4Sb12 with a record-breaking ZT = 1.5: the role of the In overfilling fraction limit and Sb overstoichiometry

Samples of indium-filled InxCo4Sb12 skutterudite with ZT ∼ 1.5 were successfully synthesized by conventional induction melting without the use of evacuated quartz ampoules.

Development of Highly Efficient Saving Processes of Rare Earth in R-T-B Permanent Magnet

In this study, cost reduction of manufacturing R (Nd, Pr, and Dy) –T (Fe, Co)-B permanent magnets was investigated. An efficient direct melting recycle of R-T-B magnet scraps and multiple methods for saving Dy were focused. In the former, Decarburization and deoxidation of R-T-B magnet scraps were developed as a pre-treatment technique for conventional induction melting. The decarburized scraps 0.001mass% carbon or less was subsequently deoxidized by calciothermic reduction. The recycled scraps can be used as low cost alloying elements by re-melting. In the latter, the casting conditions for R-T-B alloy with small admixture of Ga and the improved pulverization process of R-T-B magnet alloy were developed. Microstructure of R-T-B magnet alloy with small admixture Ga was optimized by controlling cooling rate during solidification, and its average crystalline size was to be 5μm. In order to obtain finer R-T-B magnet alloy powder preferable to the coercive force, conditions of hydrogen decrepitation (HD) prior to pulverization were optimized. Specific surface area of the HD magnet alloy was increased with decreasing temperature and hydrogen pressure, and its grindability was verified by Jet milling.

Effect of solution annealing on structure and properties of high Mo superaustenitic stainless steel castings

In the present study, the effect of solutionising temperatures of 1100, 1150, 1200 and 1250°C on the tensile strength, impact toughness and pitting corrosion of 6··5, 7··5 and 8··5 wt-%Mo cast superaustenitic stainless steels (SASS) is investigated. These alloys were produced by a conventional induction melting furnace, and subsequently, they were annealed at the above mentioned temperatures to obtain a completely austenitic structure. Thermo-Calc software was used to study the stability of secondary phases for SASS annealed at these temperatures. The increasing Mo content raises the temperature of stability of the sigma phase. Solution annealing enhances yielding toughness, as demonstrated by the increase in impact energy, and obtains the expected hardness. In addition, the pitting resistance increases with the increase in solution annealing temperatures. Quite contrary to the expectations, higher Mo containing alloys showed a tendency to pitting compared to the lower Mo containing alloy for the same set of treatment conditions. This behaviour is related to the precipitation of intermetallic phases of the heat treated alloys.

Mechanical and shape memory properties of Ni 43Co 7Mn 39Sn 11 alloy compacts fabricated by pressureless sintering

Mechanical and shape memory properties of Ni 43 Co 7 Mn 39 Sn 11 metamagnetic shape memory sintering compacts, fabricated by pressureless sintering, were investigated. With sintering time the porosity drastically decreases and the ductility is significantly enhanced compared to the samples obtained by conventional induction melting. Moreover, the fracture strain in the specimen sintered at 1173 K for 144 h is almost the same as that in the high density sintering compacts by spark plasma sintering . Interestingly, the shape memory effect decreases with decreasing porosity.

Metamagnetic shape memory effect in polycrystalline NiCoMnSn alloy fabricated by spark plasma sintering

Martensitic transformation and magnetic properties were investigated for Ni43Co7Mn39Sn11 polycrystalline specimens obtained using the spark plasma sintering method. The microstructure of the specimen sintered at 1173 K for 15 min showed only a small number of pores, and the specimen’s ductility was significantly higher than that of alloys fabricated by conventional induction melting. The martensitic and magnetic properties of the sintered specimen were basically similar to those of conventional bulk alloys. The metamagnetic shape memory effect, i.e. magnetic field-induced shape recovery, was confirmed by the magnetic field of 8 T.

Tailoring the microstructure and mechanical properties of Ti–Al alloy using a novel electromagnetic stirring method

The effect of melt convection during the solidification of Ti45Al55 alloys was investigated in terms of microstructure evolution and the resulting mechanical properties. The samples were subjected to conventional induction melting as well as enhanced melt stirring by an external magnetic field using a specially designed floating zone arrangement. The stirred samples showed a significant improvement of plastic deformability. A strong change in the morphology from dendritic to spherical and an increased properitectic phase fraction were observed after stirring.

Hydriding Properties of (Mg<SUB>1−<I>x</I></SUB>M<I><SUB>x</SUB></I>)Ni<SUB>2</SUB> C15-Type Laves Phase Alloys

Mg-based Laves phase alloys (Mg0:7M0:3)Ni2, where M elements were Ca, La, Ce, Pr, Nd and Gd were successfully developed. The alloys can be synthesized by a conventional induction melting and annealing method from intermetallic compounds MgNi2 and MNi2 as a source of Mg, Ni and M elements. The crystal structures of the major phases of annealed (Mg0:7M0:3)Ni2 alloys were C15-type for M ¼ Ca and C15b-type for M ¼ La, Ce, Pr, Nd and Gd Laves structures, respectively. In the alloys except M ¼ Ce, hydrogenation and dehydrogenation reversibly occurred. The maximum hydrogen contents of the alloys are 1.2–1.6 mass% (H/M:0.6–0.8) under hydrogen pressure of 5 MPa at 243–273 K. As the results of measurements of p-c isotherms, in the case of the M ¼ Pr and Nd, two step plateaus were clearly observed. After a few hydrogenation/dehydrogenation cycles, the alloys kept C15-type or C15b-type Laves structures without hydrogen-induced amorphization, disproportionation and decomposition. [doi:10.2320/matertrans.47.1890]

Microstructure, Metal-Mold Reaction and Fluidity of Investment Cast-TiAl Alloys

The objective of this study is to investigate the effects of mold preheating temperature on microstrcutural evolution, metal-mold reaction and fluidity of TiAl alloys. A conventional induction melting furnace was used for melting and casting of TiAl alloys in the present investigation. The previous research showed that metal-mold reaction of titanium castings was inevitable during titanium casting. However, there is no metal-mold reaction of TiAl alloys castings regardless mold materials. These results were supported by the experimental results and thermodynamic calculations. However, the grain size of TiAl alloy castings is gradually reduced with mold preheating temperature due to heterogeneous nucleation near outside of mold and diffusion of metallic element from the mold and binder. A fused Al2O3 is promising mold for investment casting of TiAl alloys because of low cost, good strength and thermal stability. The fluidity length of TiAl alloys is increasing gradually with mold preheating temperature. However, it is difficult to predict the accurate applicable limit of preheating temperature of Al2O3 mold for investment casting of TiAl alloys due to the relationship between metal-mold reaction and fluidity. Therefore, mold material, binder and mold preheating temperature are the most important process parameter of TiAl alloys investment casting.

Study on the structure and electrochemical properties of melt-spun Zr0.9Ti0.1(Ni,Co,Mn,V)2.1 alloysElectronic supplementary information (ESI) available: data used to plot Fig. 4. See http://www.rsc.org/suppdata/jm/b1/b110297d/

The structure and electrochemical properties of Zr0.9Ti0.1(Ni,Co,Mn,V)2.1 alloys prepared by both the melt-spinning method and conventional induction melting are investigated. XRD studies show that Zr0.9Ti0.1(Ni,Co,Mn,V)2.1 alloys at as-cast, melt-spinning and annealing are all face center cubic structures with a Laves C15 phase and the higher the melt-spinning rate, the greater the amorphous content. The electrochemical measurements show that melt-spun alloys have better active behavior and low discharge capacity (<270 mAh g−1). However, after annealing, the alloys are only activated completely after 30 cycles and the capacities (about 340 mAh g−1) are higher than those of as-cast and just melt-spun alloys; the annealed alloys have a better cycle stability than as-cast alloys, and the higher the melt-spinning rate, the more stable the alloy becomes.

鋳造多結晶Ｔｂ‐Ｄｙ‐Ｆｅ系合金の構造と磁歪特性

The structures and magnetostrictive properties of TbxDy1-xFe1.9 (x = 0.25, 0.30, 0.35, 0.50, 0.70) alloys prepared by a conventional induction melting and casting method were investigated. These alloys had a columnar structure in the thermal flow direction, and their grain size decreased with increasing Tb content. The magnetic and magnetostrictive properties reflected the magnitude of the magnetocrystalline anisotropy and the saturation magnetostriction. The result is related to the Tb/Dy ratio of alloys. The magnetostriction increased to more than 1500 ppm by annealing, and with decreasing the lattice spacing of the Laves phase. Grain growth was observed simultaneously.

Activation mechanism of hydrogen-storage electrode alloy Ml(NiCoMnTi) 5 produced by gas atomization

Electrochemical activation behaviour of hydrogen-storage alloy Ml(NiCoMnTi) 5 produced by conventional induction melting (CIM) and by Ar gas atomization (AGA) has been studied. It has been found that the surface oxide layer plays a minor part, while the change of energy inside alloy before and after hydriding is the major factor affecting the behaviour of activation. The larger the change of energy inside the alloy or the strain energy caused by H-atoms entering tetrahedral and octahedral sites during hydriding, the more difficult is the activation. The effect of surface oxide film on the activation could to be considered as the oxide film causing the energy of Hatoms entering the alloy to be increased, since H-atoms must consume some energy to break the surface oxide film initially, before entering the alloy.

Hydrogen storage alloy powders produced by a reduction-diffusion process and their electrode properties

Hydrogen storage alloy powders of rare-earth-based alloy-Ni systems (La-Ni, Mm-Ni-Co-Al, Mm-Ni-Co-Mn-Al; Mm = misch metal) were prepared by a reduction-diffusion process. The alloy powders were evaluated as a negative electrode in an Ni-metal hydride battery. The results are summarized as follows. (1) The alloy powder was obtained as fine particles of average particle diameter around 30 μm with smooth surface. (2) The alloy powder had uniform composition with a crystal structure of the CaCu 5 type. (3) The alloy powder exhibited good hydrogen absorption-desorption properties. The pressure plateau was very flat, not needing heat treatment. (4) The electrode properties of Mn-containing alloy powders were the same as those of alloys produced by a conventional induction melting and heat treatment process.