In the present study, the effects of magnesium on the microstructural characteristics and stress-rupture properties of the Hastelloy X superalloy were investigated. In this regard, four alloys with different amounts of magnesium (0, 17, 33, 47 ppm) were cast via the vacuum induction melting and then purified via the electro slag remelting. Microstructural observations were carried out through optical and scanning electron microscopes, and phase analysis was performed by X-ray diffraction. The stress rupture test was carried out at 815 °C/130 MPa. The results showed an almost significant effect of magnesium on decreasing grain size and sulfur content and increasing M6C carbides volume fraction. Magnesium changed the morphology of carbides from the course and continue to finely divide one. Mg segregated at the grain and carbide boundary decreases the lattice parameters of the matrix and changes the composition of M6C. Magnesium increased the rupture life by 46%. The most important causes for improving the rupture life of the Hastelloy X in the presence of magnesium are the increasing carbides volume fraction, improving its morphology, and decreasing sulfur content. تفاصيل المقالة

This study investigates the low-cycle fatigue of Nimonic105 alloy with boron and zirconium of 0.003-0.013 wt.% and 0.0-0.16 wt.%, respectively at 750 °C. The fatigue test results indicated that the alloy with boron of 0.013 wt.% had the highest fatigue life of 400 cycles, while the base alloy showed the lowest fatigue life of 21 cycles at 2% strain amplitudes. For the alloy with 0.16 wt.% Zr, and the alloy with 0.08 wt.% Zr and 0.006 wt.% B, cyclic-hardening occurred at a constant slope. Then, hardening followed a nonlinear procedure at a reducing rate. Finally, softening and fracture happened. For 0.013 wt.% Zr alloy, however, the diagram reached a stable state or slow cyclic-softening and failed after a relatively short period of cyclic -softening. The Coffin-Manson equations’ parameters verified the increased flexibility due to the addition of B. to be a factor in improving high-temperature LCF strength. The investigation of the samples’ fracture surfaces indicated that the intergranular fracture of the base alloy with the lowest fatigue life became intergranular and transgranular fracture in the alloy with 0.16 ‌wt.% Zr content and the alloy with 0.08 wt.% Zr content and 0.006 wt.% B contents. Also, 0.013 wt.% B alloy with the highest fatigue life showed a completely transgranular fracture. تفاصيل المقالة

The purpose of this study is to investigate the effects of withdrawal rate on the dendrite microstructure and its formation mechanism, the porosity, and the interaction between them in Rene 80 superalloy. So, Rene 80 Ni-base superalloy was directionally solidified on a laboratory scale using the Bridgman method. The cylindrical rods were grown at withdrawal rates of 2, 4, 6, 8, and 10 mm.min-1. Dendritic structure and solidification microporosities were evaluated in transverse and longitude sections. The results showed that when the withdrawal rate was increased, the primary and secondary dendritic arm spacing decreased. With an increasing withdrawal rate, which causes to decrease in the dendritic arms spacing, the volume fraction of inter-dendritic gamma prime was first decreased until the rate of 6 mm.min-1, and after that, its volume fraction increased. This structure results from peritectic and eutectic transformations with checkerboard-like and fan-like morphology, respectively. Moreover, the volume fraction of microporosities was minimal at the rate of 6 mm.min-1, while their average size decreased from 13.2 to 8.7 μm. The specimens were given a two-stage heat treatment followed by a stress rupture test at 191 MPa and 980˚C. It was shown that at R=6 mm.min-1, directionally solidified rods with a less solidification microporosity and well-orientated dendritic structure give higher rupture life of 25.43 hrs. تفاصيل المقالة

در این مقاله، امکان بازیابی قراضه‌های صنعتی سوپرآلیاژ IN713LC از طریق فرآیند ذوب مجدد به وسیله سرباره الکتریکی بررسی می‌گردد. هدف از این تحقیق دستیابی به ترکیب شیمیایی، ریزساختار، خواص کششی و طول عمر گسیختگی در محدوده استاندارد مطابق با استاندارد AMS5377E است. به منظور کنترل اتلاف عناصر Ti و Al، مقادیر مختلف TiO2 (0، 3 و wt% 6) به سرباره کوره با پایه 70CaF2-30Al2O3 اضافه گردید. نتایج نشان داد که در سوپرآلیاژ IN713LC با افزودن wt% TiO23 ، اتلاف عنصر Ti جبران شده و میزان گاز اکسیژن و نیتروژن در آن، به ترتیب، به ppm 3/14 و ppm 16 رسیده است. این مقدار از میزان گاز هدف (ppm 20) تعیین شده در سوپرآلیاژ IN713LC کمتر می‌باشد. همچنین، این شمش دارای بیشترین کسر حجمی فاز γ' به میزان 55% و فاز γ' ریزتر (µm 26/0) می‌باشد. با توجه به نتایج، به علت میزان بالای Al + Ti در این شمش، ریزساختار مناسبی حاصل شده است. در نتیجه‌ی تغییرات ریزساختاری، طول عمر گسیختگی این نمونه نیز در دمای ̊C 982 و تنش MPa 152 به hr 47 می‌رسد. در مقابل با افزودن TiO2 به میزان wt%6 به سرباره علاوه بر جبران اتلاف Ti، میزان Ti در شمش نیز به wt%84/0 افزایش یافته اما کسر حجمی فاز γ' کاهش یافته و خواص کششی و طول عمر نمونه نیز کاهش می‌یابد. تفاصيل المقالة