Microstructure and Oxidation Behavior of Fe-25Mn-9Al-8Ni-1C-xTi Alloy Prepared by Vacuum Arc Melting

In this study, Fe-25Mn-9Al-8Ni-1C-xTi alloy (x = 0, 0.1, 0.2, 0.3, 0.4 wt.%) was prepared by vacuum arc melting, and the corresponding microstructure and oxidation behavior at 600 °C were studied. The results show that Fe-25Mn-9Al-8Ni-1C-xTi alloy mainly contains austenite phase, ferrite phase and TiC phase. With Ti content increasing, the austenite phase content decreases, while the contents of ferrite phase and TiC phase increase. The oxidation performance test results show that the addition of Ti element greatly reduces the oxidation weight gain of the alloys at the initial oxidation stage. With the extension of the oxidation time and the further increase of the Ti content, the alloys oxidation weight gain shows a trend of first increasing and then decreasing. When the Ti content is 0.2 wt.%, the oxidation weight gain of this series of alloy reaches the lowest value during the stable oxidation period. Compared with Fe-25Mn-9Al-8Ni-1C alloy, its weight gain per unit area is reduced by 21.1%. Fe-25Mn-9Al-8Ni-1C-xTi alloy oxide layer exhibits a double-layer structure. The outer oxygen layer is mainly loose iron-oxides, while in the inner oxygen layer, the oxides are mainly composed of manganese-oxides and aluminum-oxides, which are relatively dense.

Effect of Re on the Microstructure and Mechanical Properties of NbTiZr and TaTiZr Equiatomic Alloys

The microstructure, phase composition, and mechanical properties of NbTiZr, TaTiZr, Re0.3NbTiZr, and Re0.3TaTiZr are reported. The alloys were produced by vacuum arc melting and hot isostatically pressed (HIP’d) at 1400 °C for 3 h under 276 MPa hydrostatic pressure of high-purity argon prior to testing. NbTiZr had a single-phase BCC crystal structure, while TaTiZr had a Ti- and Zr-rich BCC matrix phase and Ta-rich nanometer-sized BCC precipitates, at volume fractions of 0.49 and 0.51, respectively. Re0.3NbTiZr consisted of a BCC matrix phase and Re-rich precipitates with a FCC crystal structure and the volume fraction of 0.14. The microstructure of Re0.3TaTiZr consisted of a Zr-rich BCC matrix phase and coarse, Re and Ta rich, BCC particles, which volume fraction was 0.47. NbTiZr and TaTiZr had a room temperature (RT) yield stress of 920 MPa and 1670 MPa, respectively. While, 10 at.% Re additions increased the RT yield stress to 1220 MPa in Re0.3NbTiZr and 1715 MPa in Re0.3TaTiZr. Re also considerably improved the RT ductility of TaTiZr, from about 2.5% to 10% of true strain. The positive strengthening effect from the Re additions was retained at high (800–1200 °C) temperatures.

Effects of Zr Content on the Microstructure and Performance of TiMoNbZrx High-Entropy Alloys

TiMoNbZrx refractory high-entropy alloys were prepared by vacuum arc melting, and the influence of the Zr alloying element and its content on the phases, microstructure, mechanical properties, and wear resistance of TiMoNbZrx alloys was explored. It was found that the alloys after Zr addition were composed of a single BCC phase. Upon increasing the Zr content, the grain size of the as-cast alloy decreased first and then increased, and TiMoNbZr0.5 exhibited the smallest grain size. Adding an appropriate amount of Zr increased the strength and hardness of the alloys. TiMoNbZr0.5 exhibited the best wear resistance, with a friction coefficient of about 0.33. It also displayed the widest wear scar, the shallowest depth, and the greatest degree of wear on the grinding ball because of the formation of an oxide film during wear.

PERLAKUAN TERMOMEKANIK PADUAN TITANIUM HASIL CORAN VACCUM ARC MELTING

Titanium dan paduanya merupakan salah material logam yang tangguh, sehingga banyak diaplikasikan pada aerospace, marine, oil and gas, biomedical, olah raga, otomotif dan lain-lain. Produk Titanium, dapat diperoleh dari beberapa proses manufaktur yaitu casting, machining, forming, dan powder metallurgy. Produk akhir, ingot hasil coran ataupun produk setengah jadi paduan Titanium dapat dimodifikasi sifat mekanisnya dengan proses heat treatment dan thermomechanical treatment. Pada penelitian ini dilakukan investigasi perubahan sifat mekanis dalam hal ini kekerasan dan struktur mikro paduan titanium. Ingot paduan Titanium Ti-Al-Nb dibuat dengan proses remelting logam paduan dalam tungku busur lustrik vakum. Kemudian ingot hasil coran dilakukan proses homogenisasi pada temperatur 1100 °C selama 12 jam dengan pendinginan didalam tungku dan dilanjutkan dengan hot roll dengan pemanasan awal 1100 °C dan waktu tahan 1 jam yang kemudian dilakukan quenching. Karakterisasi paduan dilakukan pada setiap kondisi perlakuan, adapun karakterisasinya adalah pengamatan stuktur mikro menggunakan foto metalografi, SEM dan uji keras dengan metode Rockwell C. Pengamatan metalografi menunjukkan bahwa paduan merupakan alfa-beta Titanium. Proses pengulangan remelting tidak memberikan efek signifikan terhadap peningktan kekerasan paduan. Proses thermomekanikal treatment mengakibatkan perubahan bentuk mikrostruktur dari interdendritic menjadi platelike dan nilai kekerasan menjadi 52 HRc pada 3 kali remelting dan 50.5 HRc pada 5 kali remelting Kata kunci: titanium, vacuum arc melting, termomekanik, pengecoran

Study on Microstructure and In Situ Tensile Deformation Behavior of Fe-25Mn-xAl-8Ni-C Alloy Prepared by Vacuum Arc Melting

In this study, Fe-25Mn-xAl-8Ni-C alloys (x = 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%) were prepared by a vacuum arc melting method, and the microstructure of this series of alloys and the in situ tensile deformation behavior were studied. The results showed that Fe-25Mn-xAl-8Ni-C alloys mainly contained austenite phase with a small amount of NiAl compound. With the content of Al increasing, the amount of austenite decreased while the amount of NiAl compound increased. When the Al content increased to 12 wt.%, the interface between austenite and NiAl compound and austenitic internal started to precipitate k-carbide phase. In situ tensile results also showed that as the content of Al increased, the alloy elongation decreased gradually, and the tensile strength first increased and then decreased. When the Al content was up to 11 wt.%, the elongation and tensile strength were 2.6% and 702.5 MPa, respectively; the results of in situ tensile dynamic observations show that during the process of stretching, austenite deformed first, and crack initiation mainly occurred at the interface between austenite and NiAl compound, and propagated along the interface, resulting in fracture of the alloy.

Irradiation Behaviors in BCC Multi-Component Alloys with Different Lattice Distortions

Recently, the irradiation behaviors of multi-component alloys have stimulated an increasing interest due to their ability to suppress the growth of irradiation defects, though the mostly studied alloys are limited to face centered cubic (fcc) structured multi-component alloys. In this work, two single-phase body centered cubic (bcc) structured multi-component alloys (CrFeV, AlCrFeV) with different lattice distortions were prepared by vacuum arc melting, and the reference of α-Fe was also prepared. After 6 MeV Au ions irradiation to over 100 dpa (displacement per atom) at 500 °C, the bcc structured CrFeV and AlCrFeV exhibited significantly improved irradiation swelling resistance compared to α-Fe, especially AlCrFeV. The AlCrFeV alloy possesses superior swelling resistance, showing no voids compared to α-Fe and CrFeV alloy, and scarce irradiation softening appears in AlCrFeV. Owing to their chemical complexity, it is believed that the multi-component alloys under irradiation have more defect recombination and less damage accumulation. Accordingly, we discuss the origin of irradiation resistance and the Al effect in the studied bcc structured multi-component alloys.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF REFRACTORY HIGH-ENTROPY ALLOY HfMoNbTiCr

A new refractory alloy, HfMoNbTiCr, was obtained by replacing Zr with Cr or Mo in the HfMoNbTiZr or HfNbTiCrZr alloys using vacuum arc melting. The phase components, microstructures and compressive properties of the alloy in the as-cast and annealed states were investigated. The results showed that the phase components changed from a single BCC phase in HfMoNbTiZr and BCC+Laves phases in HfNbTiCrZr to multiple phases – primarily two BCC phases and two cubic Laves phases – in HfMoNbTiCr. Notably, the yield and ultimate compressive strength of the as-cast alloy significantly increased from 1719 and 1803 MPa to 1851 and 2489 MPa, without a decrease in the ductility. The stress fields induced by Mo and the Cr-containing Laves phases were responsible for the enhanced strength, while the stiff network-like framework composed of intrinsically-strong Cr-containing Laves phases may have played a vital role in retaining the ductility.

Effective Method for Preparing Low-Oxygen Titanium Ingot by Combined Powder Deoxidation and Vacuum Arc Melting Processes

In this study, an effective method is demonstrated for fabricating titanium sputtering targets, which are used to fabricate thin films in the semiconductor industry. The method is an alternative to the existing electron beam melting (EBM) process under high vacuum. Titanium sputtering targets used in the production of semiconductors must have very low concentrations of gaseous impurities, especially oxygen, as well as metal impurities. Currently, the oxygen concentration in titanium sputtering targets used for industrial purposes is less than 400 ppm. To develop an effective alternative method, powder metallurgy and melting processes were performed to prepare a low-oxygen titanium ingot with less than 400 ppm oxygen. First, titanium powder was deoxidized using calcium vapor, and then the powder was subjected to vacuum arc melting (VAM). The oxygen in the titanium powder was reduced with calcium vapor from an initial concentration of 2200 ppm to 800 ppm, and the resulting powder was melted using VAM, resulting in titanium ingots with low oxygen content, 400 ppm or less. It was also confirmed that all lattice constants, i.e., <i>d, a, c,</i> and <i>c/a</i>, decreased as oxygen concentration decreased in both the titanium powder and the ingots.