Study of the effect of Al, Cr and Sn additions on the microstructure and properties of Nb silicide based alloys

2011 ◽  
Vol 1295 ◽  
Author(s):  
P Tsakiropoulos ◽  
K Zelenitsas ◽  
N Vellios
Keyword(s):  
Heat Treatment ◽  
Phase Stability ◽  
Alloying Additions ◽  
Microstructure And Properties ◽  
Heat Treated ◽  
Cast Alloys ◽  
The Stability ◽  
Cast Microstructure

ABSTRACTThe effects of Al, Cr and Sn on segregation, microstructure, phase stability and hardness of Nb-24Ti-18Si-5X (X = Al, Cr, Sn, at%) alloys were studied. The microstructure of the as cast alloys with Cr, Al and Sn respectively contained (Nb,Ti)ss, Nb3Si, αNb5Si3 and C14-NbCr2 Laves, (Nb,Ti)ss and βNb5Si3 and (Nb,Ti)ss, Nb3Sn and Nb5Si3. The microstructures of the heat treated alloys with Al and Cr (1500 oC/100 h) contained (Nb,Ti)ss and αNb5Si3 and the alloy with Sn (1200 oC/100 h) contained (Nb,Ti)ss, Nb3Sn and αNb5Si3. Compared with Al and Cr, alloying with Sn enhanced the stability of the as cast microstructure, caused strong macrosegregation of Si and Ti, suppressed the segregation of Ti in the (Nb,Ti)ss that was promoted by Al and Cr, had the strongest effect on the macrohardness of the cast and heat treated alloys and on the vol% of the Nbss. All three alloying additions promoted the transformation of βNb5Si3 to αNb5Si3 during heat treatment and decreased the hardness of Nb5Si3 in the as cast alloys with Sn having the strongest effect and Al the weakest. After the heat treatment the hardness of Nb5Si3 increased in the alloys containing Cr and Sn and decreased in the Al containing alloy with Cr having the strongest effect.

scholarly journals A Study of the Effect of 2 at.% Sn on the Microstructure and Isothermal Oxidation at 800 and 1200 °C of Nb-24Ti-18Si-Based Alloys with Al and/or Cr Additions

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1826 ◽  
Author(s):  
Zhen Xu ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Rate Constant ◽  
Isothermal Oxidation ◽  
Primary Phase ◽  
Parabolic Oxidation ◽  
Heat Treated ◽  
Cast Alloys ◽  
The Stability ◽  
Oxidation In Air

Alloying with Al, Cr, Sn, and Ti significantly improves the oxidation of Nb silicide-based alloys at intermediate and high temperatures. There is no agreement about what the concentration of Sn in the alloys should be. It has been suggested that with Sn ≤ 3 at.% the oxidation is improved and formation of the brittle A15-Nb3Sn compound is suppressed. Definite improvements in oxidation behaviour have been observed with 5 at.% Sn or even higher concentrations, up to 8 at.% Sn. The research reported in this paper is about three model alloys with low Sn concentration and nominal compositions Nb-24Ti-18Si-5Cr-2Sn (ZX3), Nb-24Ti-18Si-5Al-2Sn (ZX5), and Nb-24Ti-18Si-5Al-5Cr-2Sn (ZX7) that were studied to understand the effect of the 2 at.% Sn addition on as-cast and heat-treated microstructures and isothermal oxidation in air at 800 and 1200 °C for 100 h. There was macrosegregation of Si and Ti in the alloys ZX3 and ZX5 and only of Si in the alloy ZX7. The Nbss was stable in all alloys. Tin and Ti exhibited opposite partitioning behaviour in the Nbss. The βNb5Si3 was the primary phase in all three cast alloys and had partially transformed to αNb5Si3 in the alloy ZX3. Aluminium in synergy with Sn increased the sluggishness of the βNb5Si3 to αNb5Si3 transformation during solidification. After the heat treatment the transformation of βNb5Si3 to αNb5Si3 had been completed in all three alloys. Fine precipitates were observed inside some αNb5Si3 grains in the alloys ZX5 and ZX7. In the latter alloys the A15-Nb3X (X = Al, Si, and Sn) formed after the heat treatment, i.e., the synergy of Al and Sn promoted the stability of A15-Nb3X intermetallic in these Nb-silicide-based alloys even at this low Sn concentration. A Nbss + Nb5Si3 eutectic formed in all three alloys and there was evidence of anomalous eutectic in the parts of the alloys ZX3 and ZX7 that had solidified under high cooling rate and/or high melt undercooling. A very fine ternary Nbss + Nb5Si3 + NbCr2 eutectic was also observed in parts of the alloy ZX3 that had solidified under high cooling rate. At 800 °C none of the alloys suffered from catastrophic pest oxidation; ZX7 had a smaller oxidation rate constant. A thin Sn-rich layer formed continuously between the scale and Nbss in the alloys ZX3 and ZX5. At 1200 °C the scales formed on all three alloys spalled off, the alloys exhibited parabolic oxidation in the early stages followed by linear oxidation; the alloy ZX5 gave the smallest rate constant values. A thicker continuous Sn-rich zone formed between the scale and substrate in all three alloys. This Sn-rich zone was noticeably thicker near the corners of the specimen of the alloy ZX7 and continuous around the whole specimen. The Nb3Sn, Nb5Sn2Si, and NbSn2 compounds were observed in the Sn-rich zone. At both temperatures the scales formed on all three alloys consisted of Nb-rich and Nb and Si-rich oxides, and Ti-rich oxide also was formed in the scales of the alloys ZX3 and ZX7 at 1200 °C. The formation of a Sn-rich layer/zone did not prevent the contamination of the bulk of the specimens by oxygen, as both Nbss and Nb5Si3 were contaminated by oxygen, the former more severely than the latter.

scholarly journals Effect of Heat Treatment on the As-Cast Microstructure and Hardness of NiSi3B2 Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 539
Author(s):  
Gonçalo M. Gorito ◽  
Aida B. Moreira ◽  
Pedro Lacerda ◽  
Manuel F. Vieira ◽  
Laura M. M. Ribeiro
Keyword(s):  
Heat Treatment ◽  
Elevated Temperatures ◽  
Casting Process ◽  
X Ray Diffraction ◽  
Heat Treated ◽  
Energy Dispersive Microanalysis ◽  
Eutectic Constituent ◽  
Backscattered Electron ◽  
Corrosion And Oxidation ◽  
Cast Microstructure

Cast Ni-Si-B alloys have the potential for high-temperature applications because of their high resistance to wear, impact, corrosion, and oxidation at elevated temperatures due to an appropriate balance of hard phases and austenite that ensures a good compromise between toughness and hardness. In this work, NiSi3B2 specimens, fabricated by the lost-wax casting process, were investigated. Given the complex multiphase cast microstructure, a differential scanning calorimeter (DSC-TGA) analysis was employed to characterize the reactions that occur during solidification and the resulting phases were characterized using scanning electron microscopy (SEM), with energy-dispersive microanalysis (EDS) and backscattered electron (BSE) image and X-ray diffraction (XRD). Due to the presence of hard phases, machining of the Ni-Si-B components can pose additional difficulties. Therefore, the conditions of the solution heat treatment, which might lead to the homogenization of the microstructure, consequently improving its machinability, were also investigated. The results of the heat-treated samples indicated that the dissolution of the eutectic constituent is accompanied by a significant decrease in the hardness (approximately 17%). It is important to emphasize that the solution heat treatments carried out reduced the hardness without affecting the percentage of borides, which will allow improving the machinability without adversely affecting the alloy performance in service.

Effect of Cooling Rate on Microstructure and Properties of Heat-Treated Fe3Al Intermetallics

2011 ◽  
Vol 189-193 ◽  
pp. 3891-3894
Author(s):  
Ya Min Li ◽  
Hong Jun Liu ◽  
Yuan Hao
Keyword(s):  
Heat Treatment ◽  
Cooling Rate ◽  
Lattice Distortion ◽  
Annealing Furnace ◽  
Microstructure And Properties ◽  
Homogenizing Annealing ◽  
Heat Treated ◽  
Mixed Fracture ◽  
Sand Mould ◽  
The Impact

The casting Fe3Al intermetallics were solidified in sodium silicate sand mould and permanent mould respectively to get different cooling rates. After heat treatment (1000°С/15 h homogenizing annealing + furnace cooling followed by 600°С/1 h tempering + oil quenching), the microstructure and properties of Fe3Al intermetallics were investigated. The results show that the heat-treated Fe3Al intermetallics at higher cooling rate has finer grained microstructure than lower cooling rate, and the lattice distortion increases due to the higher solid solubility of the elements Cr and B at higher cooling rate. The tensile strength and hardness of the Fe3Al intermetallics at higher cooling rate are slightly higher also. However, the impact power of intermetallics at higher cooling rate is 67.5% higher than that at lower cooling rate, and the impact fracture mode is also transformed from intercrystalline fracture at lower cooling rate to intercrystallin+transcrystalline mixed fracture at higher cooling rate.

The Stability of γ ’-Co3(Al,W) Phase in Co-Al-W Ternary System

2010 ◽  
Vol 654-656 ◽  
pp. 448-451 ◽  
Author(s):  
Yuki Tsukamoto ◽  
Satoru Kobayashi ◽  
Takayuki Takasugi
Keyword(s):  
Heat Treatment ◽  
Ternary System ◽  
Microstructural Evolution ◽  
Treatment Time ◽  
Bulk Alloy ◽  
Epma Analysis ◽  
Heat Treated ◽  
Cold Rolled ◽  
The Stability ◽  
Couple Method

The thermodynamic stability ’- Co3(Al,W) phase (L12) in the Co-Al-W ternary system at 900 °C was investigated through microstructure and EPMA analysis on a heat-treated bulk alloy. To promote microstructural evolution, the bulk alloy was cold rolled before heat treatment. By heating at 900 °C, the ’ phase was formed discontinuously in contact with the -Co (A1) phase. With increasing heat treatment time, however, the fraction of ’ phase decreased while that of , CoAl (B2) and Co3W (D019) phases increased. These results are consistent with our previous work with a diffusion-couple method, indicating that the ’ phase is metastable, and the three phases of, CoAl and Co3W are thermodynamically stable at 900 °C.

Preparation of YBa2Cu3O7−y films on SrTiO3 and MgO by the dipping-pyrolysis process under low-p(O2) heat treatment

1992 ◽  
Vol 7 (9) ◽  
pp. 2337-2342 ◽  
Author(s):  
T. Manabe ◽  
K. Arai ◽  
W. Kondo ◽  
S. Mizuta ◽  
T. Kumagai
Keyword(s):  
Heat Treatment ◽  
Stability Region ◽  
Pyrolysis Process ◽  
Axis Orientation ◽  
Ag Addition ◽  
Upper Limit ◽  
Treatment Conditions ◽  
Heat Treated ◽  
The Stability ◽  
Annealing Method

Superconducting YBa2Cu3O7−y (YBCO) films having a thickness of 1 μm were prepared on SrTiO3(100) and MgO(100) by the dipping-pyrolysis process using a low-p(O2) annealing method. Heat-treatment conditions were varied along the upper limit of the stability region of the YBCO phase. Films on SrTiO3(100) exhibited strong c-axis orientation with sharp rocking curves (FWHM = 0.8°). The highest Tc,zero of 87 K was obtained for the film heat-treated at 750 °C. On the other hand, films on MgO(100) showed broader rocking curves and their Tc's remained lower. Moreover, Ag addition was found to enhance the Tc values (Tc,zero = 91 K) of films on SrTiO3 heat-treated at 750 °C.

Phase Stability of Sigma + Beta Microstructures in the Ternary Nb-Ti-Al System

1990 ◽  
Vol 194 ◽  
Author(s):  
D. T. Hoelzer ◽  
F. Ebrahimi
Keyword(s):  
Phase Stability ◽  
Orthorhombic Phase ◽  
Beta Phase ◽  
Phase Region ◽  
Nominal Composition ◽  
Two Phase ◽  
Σ Phase ◽  
Β Phase ◽  
Heat Treated ◽  
The Stability

AbstractAn alloy with the nominal composition 42Nb-28Ti-30Al (at.%) was heat treated in the sigma + beta phase region. The evolution of σ phase from the metastable β phase and the stability of the two-phase microstructure at various aging temperatures were evaluated using TEM techniques. The results indicate that the β phase in equilibrium with the σ phase at high temperatures decomposes to the orthorhombic phase at temperatures below 1200°C.

Microstructure and Properties of Welds of Semi-Austenitic Precipitation Hardening Stainlees Steel after Heat Treatment

2013 ◽  
Vol 58 (2) ◽  
pp. 613-617 ◽  
Author(s):  
A. Ziewiec ◽  
E. Tasak ◽  
M. Witkowska ◽  
K. Ziewiec
Keyword(s):  
Heat Treatment ◽  
Welded Joints ◽  
Electron Microscope Study ◽  
Precipitation Hardening ◽  
Welded Joint ◽  
Inert Gas ◽  
Scanning Electron Microscope Study ◽  
Microstructure And Properties ◽  
Heat Treated ◽  
Δ Ferrite

This paper presents the studies of the microstructure and properties of the welded joints made of 15-7Mo precipitation hardened semi-austenitic stainless steel welded by Tungsten Inert Gas. Microstructural changes in the heat treated welded joints was assessed. It was found that the joints of 15-7Mo steel in as welded state contain martensite, austenite and δ-ferrite. Scanning electron microscope study of the joints was carried out. The sub-zero and destabilization heat treatment were found to decrease or completely eliminate the austenite in the microstructure and increase hardness of the welded joint.

Design and Evaluation of Carbon Nanotube Based Nanofluids for Heat Transfer Applications

2013 ◽  
Vol 1543 ◽  
pp. 143-148
Author(s):  
Sathya P. Singh ◽  
Nader Nikkam ◽  
Morteza Ghanbarpour ◽  
Muhammet S. Toprak ◽  
M. Muhammed ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Rheological Properties ◽  
Gum Arabic ◽  
Step Method ◽  
Potential Measurement ◽  
Heat Treated ◽  
Electron Microscopy Analysis ◽  
Predicted Values ◽  
The Stability ◽  
Ph Range

ABSTRACTThe present work investigates the fabrication, thermal conductivity (TC) and rheological properties of water based carbon nanotubes (CNTs) nanofluids (NFs) prepared using a two-step method. As-received (AR) CNTs heated and the effect of heat treatment was studied using X-ray diffraction and thermogravimetric analysis. The AR-CNTs and heat-treated CNTs (HT-CNTs) were dispersed with varying concentration of surface modifiers Gum Arabic (GA) and TritonX-100 (TX) respectively. It was found that heat treatment of CNTs effectively improved the TC and influenced rheological properties of NFs. Scanning electron microscopy analysis revealed TX modified NFs showed better dispersion ability compared to GA. Surface modification of the CNTs was confirmed by Fourier Transformation Infrared (FTIR) analysis. Zeta potential measurement showed the stability region for GA modified NFs in the pH range of 5-11, whereas pH was between 9.5-10 for TX NFs. The concentration of surface modifier plays an extensive role on both TC and rheological behavior of NFs. A maximum TC enhancement of 10% with increases in viscosity around 2% for TX based HT-CNTs NFs was measured. Finally comparison of experimental TC results with the predicted values obtained from a model demonstrated inadequacy of the predictive model for CNT NFs system.

Effect of Heat-Treatment on the Microstructure and Properties of SiO2-TiO2 Aerogels Synthesized via Supercritical Drying

2016 ◽  
Vol 848 ◽  
pp. 770-776 ◽  
Author(s):  
Yong Gang Jiang ◽  
Yan Qing Qin ◽  
Jun Zong Feng ◽  
Jian Feng ◽  
Lin Xu
Keyword(s):  
Heat Treatment ◽  
Specific Surface ◽  
Three Dimensional ◽  
Supercritical Drying ◽  
High Specific Surface Area ◽  
Sem Images ◽  
Average Pore ◽  
Microstructure And Properties ◽  
Surface Areas ◽  
Heat Treated

Monolithic SiO2-TiO2 aerogels were prepared via supercritical drying using tetraethoxysilane and tetrabutyltitanate as precursors and ethanol as solvent. Influence of the heat-treatment on the microstructure and properties of SiO2-TiO2 aerogels were investigated in detail. The results showed that the as-prepared SiO2-TiO2 aerogels had low densities, high specific surface areas, small average pore diameters, and three-dimensional nanoporous structures. The anatase TiO2 phase of SiO2-TiO2 aerogels could form during supercritical drying process, and the transition to rutile TiO2 phase occurred after experiencing 1200°C for 2 h. SiO2-TiO2 aerogels containing 30 wt% TiO2 (ST3) still presented relatively high specific surface area of 451 m2/g even they undergo the treatment of 1000°C for 2 h. And the SEM images indicated that the agglomerated particles derived from ST3 appeared gradually to some extent. The glassy luster of ST3 heat-treated at 1200°C for 2 h illuminates SiO2 started to vitrify. Besides, the thermal conductivity of ST3 at room temperature is up to 0.03257 W·m-1·K-1.

scholarly journals Effect of Artificial Aging Treatment and lubrication Modes on the Machinability of A356 Cast Alloys

2019 ◽  
Author(s):  
Mohamed Amine Alliche ◽  
Abdelhakim Djebara ◽  
Yasser Zedan ◽  
Victor Songmene
Keyword(s):  
Heat Treatment ◽  
Cutting Force ◽  
Surface Quality ◽  
Feed Rate ◽  
Artificial Aging ◽  
Cutting Speed ◽  
Chip Thickness ◽  
Burr Formation ◽  
Heat Treated ◽  
Cast Alloys

This article discuss the effects of heat treatment on the machinability of Al-Si-Mg alloys (A356) cast alloys for as-received alloy, solution heat-treated alloy (SHT) as well as solution heat treated and then aged alloys at 155ºC, 180ºC, and 220ºC. In the course of machinability evaluation, several criteria including cutting force, surface roughness, tool wears and burr analysis (chip) were studied. The results and analysis in this work indicated that selected machinability criteria are important and necessary to effectively evaluate the machinability of A356 alloys. Machinability of both materials and tool was estimated in terms of chip thickness ratio and burr formation, roughness, cutting force and flank wear. The effects of various lubrication modes such as dry, mist and wet, cutting parameters, including cutting speed and feed rate on the machinability of A356 cast alloys were also examined. Experimental results proves that the heat treatment parameters strongly controlling the burr formation and surface quality. The results obtained indicate that better drilling performance in terms of surface quality occurs at high feed rate, dry drilling and artificial aging at T6.

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