Plasma Arc Melting Research Articles

Microstructure of TiN-TiB2 Composites Prepared by Spark Plasma Sintering and Arc Melting

Microstructure of TiN-TiB2 Composites Prepared by Spark Plasma Sintering and Arc Melting

Hydrogen effect on refining of Mo metal by Ar–H2 plasma arc melting

The refining effect of Ar/Ar–H2 plasma arc melting (PAM) was investigated and the purity of Mo metals was evaluated by glow discharge mass spectrometry (GDMS). Most impurities in the Mo metals except for W were removed by Ar/Ar–H2 PAM down to a few mass ppm levels, and the purities of respective Mo metals refined by Ar/Ar–20%H2 PAM were improved up to 4N(99.9943%) and 5N(99.9996%). It is also found that Ar–H2 PAM provides excellent decarburization, deoxidation, and denitrogenization. This confirmed that the refining effect is chemically induced by activated hydrogen atoms during Ar–H2 PAM.

Directional solidification of Ti-45Al-8Nb-(W,B,Y) alloy

Using a Bridgman vertical vacuum furnace, Ti-45Al-8Nb-(W,B,Y) (at.%) bars, which were prepared from a plasma arc melting (PAM) ingot, were directionally solidified at growth rates of 10, 15, and 20 μm/s. Polysynthetic twinned (PST) crystal with an aligned lamellar microstructure was obtained at the growth rate of 15 μm/s because of high Nb addition. The principle of PST crystal growth and the effect of Nb element were discussed. The results of investigations on microstructure and micromechanical properties of the directionally solidified (DS) bars of Ti-45Al-8Nb-(W,B,Y) alloy are briefly summarized.

Preparation of High-Purity Cobalt by Anion-Exchange Separation and Plasma Arc Melting

High-purity Co was prepared with valence-controlled anion-exchange separation, oxidation refining using plasma arc melting, and H2-Ar plasma arc melting on a pilot scale. The result of a laboratory-scale experiment indicated that the slower flow rate is more effective to remove the impurities by anion-exchange separation. However, the separation efficiency is reduced by scaling up the column from the laboratory to pilot scale. The discussion of the decrease in the separation efficiency implies that the distribution coefficient increases as the concentration of the adsorbate is lowered, but a reduced slower flow rate might increase the final purity of Co. In addition to anion-exchange separation, Co oxidation refining using plasma arc melting was useful. Consequently, a high-purity Co of 99.9998 pct by mass excluding gaseous elements was prepared, which represents the highest purity reported.

Refining effect of hydrogen plasma arc melting on titanium sponges

Hydrogen plasma arc melting (HPAM) of commercial Ti sponges (> 99.7%) was examined. Ti sponges had main impurities such as Fe, Al, Cl and Mn. These main impurities could be reduced more efficiently by HPAM than by Ar PAM. Other small amount of impurities also had a tendency of reduction by HPAM. In addition, it was found that each removal degree is attributable to a differential refining effect caused by the difference of initial impurity concentration. For the unique refining effect of HPAM, dissociated and activated hydrogen atoms involved in the high temperature plasma arc are considered to play an important role in the melting process.

Mass Production of High-Purity Iron Using Anion-Exchange Separation and Plasma Arc Melting

High-purity Fe was manufactured using anion-exchange separation (AES), oxidation refining, and hydrogen-argon plasma arc melting. As a result, the purity of Fe achieved 99.9993 mass pct. Two issues have been improved: the decrease in the refining efficiency in AES was solved by the decrease in the flow rate, and W contamination during plasma arc melting was solved by the increase in the cooling efficiency of W-ThO2 cathode.

Purity Evaluation of Ta Metal Refined by Ar/Ar-H2 Plasma Arc Melting

The refining effect of Ar/Ar-H2 plasma arc melting (PAM) was investigated and the purity of Ta metals was evaluated by glow discharge mass spectrometry (GDMS). Most impurities in the Ta metals were removed by Ar/Ar-H2 PAM, down to a few mass ppm levels, and the purities of respective Ta metals refined by Ar/Ar-20% PAM were improved up to 5N5 (99.9995 %) and 5N7 (99.99972 %). It was also found that the deoxidation reaction under hydrogen plasma condition is enhanced by a remarkable decrease in the oxygen concentration of the Ta metal refined by Ar-H2 PAM.

Oxidation refining of iron using plasma-arc melting

Oxidation refining of Fe using plasma arc melting, by the addition of iron oxide as an oxidizing agent, has been carried out. In this refining process, an impurity element which has higher affinity for oxygen than iron was expected to be eliminated. As the result, decreases in Si, Mn, Al, Ca, Ga, and Zr were observed and 99.996 mass% of iron could be obtained from 99.93 mass% of electrolytic iron by plasma arc melting under oxidizing conditions followed by argon–hydrogen plasma arc melting. Specifically, the removal of Si was found to proceed by the distribution between in the liquid Fe phase and in the oxide phase. In addition, the relation of Si and oxygen concentration in liquid iron was consistent with the data in the literature.

Preparation of 5N grade tantalum by electron beam melting

Abstract The commercial Na-reduced tantalum powder was purified using electron beam melting (EBM) by four successive melt cycles. Nearly 60 impurity elements (Li to U) in the tantalum was analyzed using glow discharge mass spectrometry (GDMS). Vickers hardness on the surface of the electron beam (EB)-melted tantalum piece was decreased by ∼43% after first melting and the change in hardness was feeble in the subsequent melt cycles, indicating a quick vaporization of impurities during the first melt cycle itself. The behaviour of Na, K, S, Ti, Mo, Zr, Nb, W, C, N, and O impurities in tantalum at the end of each melt cycle were analyzed and found to be in ppm/ppb level. The overall purity of tantalum by EBM was increased from 2N8 to 5N at the end of three melt cycles. GDMS analysis results on EB-melted tantalum, showed excellent removal effect of interstitial and metallic impurities. The metallic and gaseous impurities present in high purity of tantalum prepared by EBM and plasma arc melting (PAM) were compared. The removal degree of impurities in tantalum using EBM was much higher, when compared to Ar/Ar–H 2 plasma arc melting.

Effect of Ar/Ar-H<SUB>2</SUB> Plasma Arc Melting on Cu Purification

Removal of impurities from Cu metal by Ar and Ar-20%H2 plasma arc melting (PAM) has been carried out. Several impurities such as Li, Na, Mg, P, S, Cl, K, Ca, Zn, Pd, Pb and Bi in Cu were efficiently removed when only Ar plasma gas was used. Moreover, removal degrees for the above mentioned impurities were significantly increased after Ar-20%H2-PAM, especially for K, Zn and Pd. It was found that Ar-H2 PAM showed an excellent effect to eliminate impurities with higher vapor pressures than that of Cu metal. [doi:10.2320/matertrans.MRA2008054]

Melting Decontamination of Radioactive Scrap Metal by Graphite Arc Melter

The partitioning phenomena of radioisotope cobalt-60 (60Co) and cesium-137 (137Cs) from a molten ingot, slag, and dust have been investigated for the effect of the slag type, slag concentration and basicity in a plasma arc melting process. A direct current plasma arc furnace was used to melt contaminated stainless steel, and mild steel with an acid, neutral, and basic slag (SiO2, CaO, Al2O3, Fe2O3, MgO) containing radioactive 60Co and 137Cs, to measure the partitioning phenomena. Calcium oxide and ferric oxide were added to provide an increase in the slag fluidity and oxidative potential, respectively. Most of the 60Co remained in the ingot phase and was barely present in the slag. 60Co decontamination factor was not highly dependent on the slag composition. The distribution ratio of 60Co the ingot and the slag phase showed that about 90% to 95% was recovered in the ingots. 137Cs was completely eliminated from the melt of the stainless steel as well as the carbon steel, and was distributed to the slag and dust phase. The partition remaining in the slag depended on whether the slag was basic or acidic and had a high oxidative flux (Fe2O3). A maximum of 52% of the 137Cs remained in the slag phase with an acid slag.

Thermodynamic Calculation of Alpha-Case Formation in Titanium Alloys

The alpha-case formation mechanism was elucidated for the economic titanium casting. The α-case formation reaction between Ti and Al2O3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by electron probe micro-analyzer and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold was not able to be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, from our experimental results and thermodynamic calculations and Calphad modeling (Thermo-calc®), it was confirmed that the α-case is formed not only by an interstitial element but also by substitutional metallic elements dissolved from mold materials. Our newly established α-case formation mechanism will surely lead to a variety of significant applications of the α-case controlled Ti casting.

In Situ Synthesis of TiAl Matrix Composites by Melting Route

TiAl alloys Al composition range between 45 and 49 at%, includes γ-TiAl and α2-Ti3Al, are an emerging high temperature materials which has higher specific strength, oxidation ratio and specific modulus than Ni base superalloy. In this study, TiAl alloys were manufactured by plasma arc melting (PAM) and then TiAl and granular boron carbide were in-situ synthesized in PAM method again. The in-situ synthesized TiAl matrix composites were investigated by using X-ray diffractometer, optical microscope, and electron probe micro-analyzer.

Titanium and Titanium Alloy Castings for Biomedical Application

The aim of this study is to optimize the economic net-shape forming of titanium and titanium alloys for the biomedical application. The alpha-case formation reaction between titanium, and Al2O3, ZrO2, CaO stabilized ZrO2 and ZrSiO4 mold were examined in a plasma arc melting furnace. Regardless of the thermodynamic approach, α-case formation reactions still remain to be eliminated with the complex chemical milling processes. The reason why the α-case generated cannot be explained by the conventional α-case formation mechanism. However, from the experimental results and thermodynamic consideration, it can be confirmed that the α-case is formed not only by interstitial oxygen atoms but also by substitutional metal atoms dissolved from mold materials. Based on the interstitial and substitutional α-case formation mechanism, α-case controlled net-shape forming of titanium and titanium alloys can be possible for the biomedical application.

Titanium Alloys Casting for Structural Application

The aim of this study is to clarify the metal-mold reaction for the economic net-shape forming of titanium and titanium alloys. The metal-mold reactions between pure titanium, TiAl alloys and Al2O3 mold were examined in a plasma arc melting furnace. The alpha-case generation between pure titanium and Al2O3 mold could not be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, based on the interstitial and substitutional α-case formation mechanism, the α-case formation between pure titanium and Al2O3 mold, and α-case free casting of TiAl alloys against Al2O3 mold can be explained. On the basis of the interstitial and substitutional α-case formation mechanism, α-case controlled net-shape forming of titanium and TiAl alloys can be possible for the structural materials.

Tensile Properties and Creep Behavior of Compositional Modified Orthorhombic Ti<sub>2</sub>AlNb Alloys

Several beta stabilizing elements such as Mo, Cr, W, V and Fe have been added to Ti- 22Al-27Nb alloy for substituting a portion of Nb in order to further improve the tensile properties and creep resistances of orthorhombic Ti2AlNb-based alloys. Six compositional modified alloys Ti- 22Al-19.2Nb-2Cr, Ti-22Al-12.5Nb-2W-2Cr, Ti-22Al-10.8Nb-2Mo-2Cr, Ti-22Al-16Nb-2Cr-2V, Ti-22Al-11Nb-2Mo-1Fe, Ti-22Al-16.3Nb-2V-1Fe were prepared by plasma arc melting. The phase constitutions of these alloys were found to be B2+O or B2+O+α2 phases. The tensile properties were investigated at room temperature, and the creep behaviors were investigated under 650oC/310MPa and 650 to 750oC/200MPa. The results showed that Mo+Fe and W+Cr addition improved effectively the 0.2% yield strength and creep resistance. Ti-22Al-11Nb-2Mo-1Fe alloy exhibited the lower transient creep strain and steady-state creep rate, and longer 1% creep-strain lifetime than Ti-22Al-27Nb alloy at 650 to 700oC creep. The dislocation-controlled creep deformation mechanism was suggested to the creep behaviors of the Mo+Fe-modified alloy.

Refining Effect of Hydrogen Plasma Arc Melting and Trace Impurity Analysis by Glow Discharge Mass Spectrometry

ABSTRACT Recently, hydrogen plasma arc melting (HPAM) has been expected to be a practical melting and refining technique for metals and alloys. The effect of H2 addition to the Ar plasma gas on the purification of metals and alloys has been described by possible chemical reactions of impurities with activated hydrogen atoms on a molten metal as well as the increase in temperature of a metal surface. Trace impurity concentration of refined metals is determined using glow discharge mass spectrometry (GDMS). This method is used to determine trace elements quantitatively because GDMS is a direct solid-state analytical method that uses no chemical process and provides reliable quantitative concentrations for most elements below 0.01 ppm. We reviewed the refining effect of HPAM for several metals by trace impurity analysis using GDMS.

ICONE15-10596 CHARACTERISTICS OF URANIUM DISTRIBUTION DURING THE METAL MELTING IN AN ELECTRIC ARC FURNACE

The distribution of cerium (Ce) and uranium (U) in the ingot, slag and dust phases has been investigated for the effects of the slag type, slag concentration and basicity in a plasma arc melting process. A direct current plasma arc furnace was used to melt contaminated stainless steel and real wastes from the uranium conversion plant in KAERI. The slag former used to remove the contaminants mainly consists of silica (SiO_2), calcium oxide (CaO) and aluminum oxide (Al_2O_3). Calcium fluoride (CaF_2), nickel oxide (NiO), and ferric oxide (Fe_2O_3) were added to provide an increase in the slag fluidity and oxidative potential respectively. The cerium was used as the surrogate of the uranium because the thermochemical and physical properties of the cerium were greatly similar to those of the uranium. The cerium was removed from ingot phase to slag phase by up to 99%. The removal ratio of the cerium was increased with an increase of the amount of the slag former. And maximum removal of the cerium occurred when the slag basicity was 0.82. The natural uranium (UO_2) was partitioned from the ingot phase to the slag phase by up to 95%. The distribution of the natural uranium was considerably dependent on the basicity of the slag former and the composition of slag former. The optimum condition for the removal of the uranium was about 1.5 in basicity and 15wt% of slag former. According to the increase of the amount of the slag former, the distribution of uranium oxide linearly increased due to the increase of the capacity to capture uranium oxide within the slag. Through experiments with the various slag former, we verified that the slag formers containing calcium fluoride (CaF_2) and high silica were more effective for the melting decontamination of stainless steel wastes contaminated with uranium. In the melting tests with stainless steel wastes from the uranium conversion plant in KAERI, we found that the results of the uranium decontamination were mostly similar to those of the uranium oxide.

Thermodynamic estimation of hydride formation during hydrogen plasma arc melting

The purification effect by hydrogen plasma arc melting (HPAM) and the respective probabilities of hydride formation for several metals were investigated. Commercially pure Fe, Cr, Ti, V, Zr, Nb, and Ta metals were melted for 60 min using Ar–30 vol% H 2 plasma gas at 5.3 kPa (Ta at 101.3 kPa). Results showed that the degree of removal of each impurity in the metals increases concomitant with the increased vapor pressure difference between the impurity and the metal. This study further established that addition of hydrogen to the plasma gas increases the metal surface temperature, which is a main reason for the superior purification provided by Ar–H 2 plasma arc melting. Thermodynamic calculations showed that the main part of impurities transfers to the gas phase as atomic species, whereas Sb can predominantly form hydrides over other corresponding atomic species.

Investment Casting of Ti Alloys for Biomedical Application

The aim of this study is to clarify the alpha-case formation mechanisms for the economic net-shape forming of Ti and Ti alloys. The α-case formation reaction between Ti and Al2O3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by using an electron probe micro-analyzer and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold could not be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, on the basis of our experimental results and thermodynamic consideration, it was confirmed that the α-case is formed not only by interstitial oxygen atoms but also by substitutional metal atoms dissolved from mold materials. Based on the α-case formation mechanism, α-case free net-shape forming of Ti and Ti alloys could be possible for biomedical applications.