scholarly journals On the Microstructure and Properties of Nb-18Si-6Mo-5Al-5Cr-2.5W-1Hf Nb-Silicide Based Alloys with Ge, Sn and Ti Additions (at.%)

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4548
Author(s):  
Jiang Zhao ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
Chemical Composition ◽  
Creep Rate ◽  
Design Methodology ◽  
Volume Fraction ◽  
Isothermal Oxidation ◽  
Weight Changes ◽  
Parabolic Oxidation ◽  
Low Volume

We studied the microstructures and isothermal oxidation of the Nb-silicide-based alloys Nb-11.5Ti-18Si-5Mo-2W-4.9Sn-4.6Ge-4.5Cr-4.7Al-1Hf (JZ4) and Nb-21Ti-18Si-6.7Mo-1.2W-4.4Sn-4.2Ge-4Cr-3.7Al-0.8Hf (JZ5), calculated their average creep rate for the creep goal conditions of T = 1200 °C and σ = 170 MPa, and compared properties of the two alloys with those of other refractory metal (RM) complex concentrated alloys (RCCAs). Both alloys had a density less than 7.3 g/cm3 and lower than the density of multiphase bcc solid solution + M5Si3 silicide RCCAs. There was macrosegregation of Si in both alloys, which had the same phases in their as-cast microstructures, namely βNb5Si3, αNb5Si3, A15-Nb3X (X = Al, Ge, Si, Sn), TM5Sn2X (X = Al, Ge, Si), C14-Cr2Nb, but no solid solution. After heat treatment at 1500 °C for 100 h, a low volume fraction of a W-rich (Nb, W)ss solid solution was observed in both alloys together with βNb5Si3, αNb5Si3 and A15-Nb3X but not the TM5Sn2X, whereas the Laves phase was observed only in JZ4. At 800 °C, both alloys did not pest, and there was no spallation of their scales at 1200 °C. At both temperatures, both alloys followed parabolic oxidation kinetics and their weight changes were lower than those of Ti-rich Nb-silicide-based alloys. The oxidation of both alloys was superior to that of other RCCAs studied to date. For each alloy the Si macrosegregation, volume fraction of solid solution, chemical composition of solid solution and Nb5Si3, and weight changes in isothermal oxidation at 800 and 1200 °C that were calculated using the alloy design methodology NICE agreed well with the experimental results.

scholarly journals On the Microstructure and Properties of Nb-12Ti-18Si-6Ta-5Al-5Cr-2.5W-1Hf (at.%) Silicide-Based Alloys with Ge and Sn Additions

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3719
Author(s):  
Jiang Zhao ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Design Methodology ◽  
Isothermal Oxidation ◽  
Chemical Compositions ◽  
Weight Changes ◽  
Parabolic Oxidation ◽  
Goal Condition ◽  
Heat Treated ◽  
Order Of Magnitude ◽  
Solution Volume

The microstructures and properties of the alloys JZ3 (Nb-12.4Ti-17.7Si-6Ta-2.7W-3.7Sn-4.8Ge-1Hf-4.7Al-5.2Cr) and JZ3+(Nb-12.4Ti-19.7Si-5.7Ta-2.3W-5.7Sn-4.9Ge-0.8Hf-4.6Al-5.2Cr) were studied. The densities of both alloys were lower than the densities of Ni-based superalloys and many of the refractory metal complex concentrated alloys (RCCAs) studied to date. Both alloys had Si macrosegregation and the same phases in their as cast and heat treated microstructures, namely βNb5Si3, αNb5Si3, A15-Nb3X (X = Al, Ge, Si, Sn), C14-Cr2Nb and solid solution. W-rich solid solutions were stable in both alloys. At 800 °C only the alloy JZ3 did not show pest oxidation, and at 1200 °C a thin and well adhering scale formed only on JZ3+. The alloy JZ3+ followed parabolic oxidation with rate constant one order of magnitude higher than the single crystal Ni-superalloy CMSX-4 for the first 14 h of oxidation. The oxidation of both alloys was superior to that of RCCAs. Both alloys were predicted to have better creep at the creep goal condition compared with the superalloy CMSX-4. Calculated Si macrosegregation, solid solution volume fractions, chemical compositions of solid solution and Nb5Si3, weight changes in isothermal oxidation at 800 and 1200 °C using the alloy design methodology NICE agreed well with the experimental results.

High Temperature Compression Properties of Ni3(Si,Ti) Based Intermetallic Compounds

2014 ◽  
Vol 783-786 ◽  
pp. 1129-1135
Author(s):  
Takehito Hagisawa ◽  
Hirokazu Madarame ◽  
Shinji Tanaka ◽  
Yasuyuki Kaneno ◽  
Takayuki Takasugi
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
High Temperature ◽  
Strain Rate ◽  
Volume Fraction ◽  
Solution Phase ◽  
Solid Solution Phase ◽  
Ti Alloy ◽  
Compression Properties ◽  
Ti Alloys

High temperature compression properties of Al-, Cr-or Nb-added Ni3(Si,Ti) based intermetallic compounds were investigated by uni-axial compression test and microstructural observation. The Al-or Cr-added Ni3(Si,Ti) alloys after homogenization heat treatment exhibited a two-phase microstructure consisting of L12and Ni-solid solution phases. The Nb-added Ni3(Si,Ti) alloy after homogenization heat treatment exhibited a triple-phase microstructure consisting of G-phase with D8a structure and Ni-solid solution phase in the L12matrix. The volume fraction of Ni-solid solution phase increased in order of Cr-, Nb-and Al-added Ni3(Si,Ti) alloys. The Cr-added Ni3(Si,Ti) alloy was deformable at high strain rate, while the Nb-added one was deformable at low strain rate. It can be considered that the deformability of Ni3(Si,Ti) at high temperature is closely correlated with volume fraction of Ni-solid solution phase and recrystallization behavior.

scholarly journals On the Microstructure and Properties of Nb-Ti-Cr-Al-B-Si-X (X = Hf, Sn, Ta) Refractory Complex Concentrated Alloys

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7615
Author(s):  
Tophan Thandorn ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Chemical Composition ◽  
Refractory Metal ◽  
Design Methodology ◽  
Alloy Design ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Specific Strength ◽  
Heat Treated ◽  
Intermetallic Composite

We studied the effect of the addition of Hf, Sn, or Ta on the density, macrosegregation, microstructure, hardness and oxidation of three refractory metal intermetallic composites based on Nb (RM(Nb)ICs) that were also complex concentrated alloys (i.e., RM(Nb)ICs/RCCAs), namely, the alloys TT5, TT6, and TT7, which had the nominal compositions (at.%) Nb-24Ti-18Si-5Al-5B-5Cr-6Ta, Nb-24Ti-18Si-4Al-6B-5Cr-4Sn and Nb-24Ti-17Si-5Al-6B-5Cr-5Hf, respectively. The alloys were compared with B containing and B free RM(Nb)ICs. The macrosegregation of B, Ti, and Si was reduced with the addition, respectively of Hf, Sn or Ta, Sn or Ta, and Hf or Sn. All three alloys had densities less than 7 g/cm3. The alloy TT6 had the highest specific strength in the as cast and heat-treated conditions, which was also higher than that of RCCAs and refractory metal high entropy alloys (RHEAs). The bcc solid solution Nbss and the tetragonal T2 and hexagonal D88 silicides were stable in the alloys TT5 and TT7, whereas in TT6 the stable phases were the A15-Nb3Sn and the T2 and D88 silicides. All three alloys did not pest at 800 °C, where only the scale that was formed on TT5 spalled off. At 1200 °C, the scale of TT5 spalled off, but not the scales of TT6 and TT7. Compared with the B free alloys, the synergy of B with Ta was the least effective regarding oxidation at 800 and 1200 °C. Macrosegregation of solutes, the chemical composition of phases, the hardness of the Nbss and the alloys, and the oxidation of the alloys at 800 and 1200 °C were considered from the perspective of the Niobium Intermetallic Composite Elaboration (NICE) alloy design methodology. Relationships between properties and the parameters VEC, δ, and Δχ of alloy or phase and between parameters were discussed. The trends of parameters and the location of alloys and phases in parameter maps were in agreement with NICE.

Study on Microstructure and Properties of Mg-9Al-xZn Alloys

2005 ◽  
Vol 475-479 ◽  
pp. 477-480
Author(s):  
Xi Yan Zhang ◽  
Feng Jiang ◽  
Shi-jie Zhou ◽  
Chong Jia ◽  
Min Zhao ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
Corrosion Resistance ◽  
Chemical Composition ◽  
Close Relation ◽  
Microstructure And Properties ◽  
Solid Solution Strengthening ◽  
Mg17al12 Phase ◽  
Solution Strengthening ◽  
Zn Alloys

Some Zn and a little Ag are added into ZM5 magnesium alloy (one of Mg-9 wt%Al-1 wt%Zn alloys in China), and the differences of the microstructures and properties between the new alloy and ZM5 is investigated. Effects of heat treatment and alloying elements (Zn and Ag) on the microstructure and tensile properties of Mg-9Al-xZn alloys, and relationships between the chemical composition, microstructure and properties are investigated. Zn ad Ag have obvious solid solution strengthening effects on Mg-9Al-xZn alloy, while Ag is detrimental to the corrosion resistance after being artificial aged. The morphology of pearlite-like secondary γ(Mg17Al12) phase (γII) has close relation with the properties.

scholarly journals On the Microstructure and Isothermal Oxidation at 800 and 1200 °C of the Nb-24Ti-18Si-5Al-5Cr-5Ge-5Sn (at.%) Silicide-Based Alloy

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 722 ◽  
Author(s):  
Ofelia Hernández-Negrete ◽  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Oxidation Resistance ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Cast Alloy ◽  
Isothermal Oxidation ◽  
Valence Electron Concentration ◽  
Scale Spallation ◽  
Substrate Interface ◽  
Oxidation In Air

The research presented in this paper aspired to understand how the simultaneous addition of Ge and Sn in an Hf-free Nb-silicide-based alloy affected its oxidation resistance. Results are presented for the Nb-24Ti-18Si-5Al-5Cr-5Ge-5Sn alloy (at.%) which was studied in the as-cast and heat-treated (1400 °C/100 h) conditions and after isothermal oxidation in air at 800 and 1200 °C. There was macrosegregation in the cast alloy, in which the Nbss formed at a low volume fraction and was not stable after heat treatment at 1400 °C. The βNb5Si3, A15-Nb3Sn, and C14-NbCr2 were stable phases. The alloy did not undergo pest oxidation at 800 °C, and there was no spallation of its scale at 1200 °C. There was enrichment in Ge and Sn in the substrate below the scale/substrate interface, where the compounds Nb3Sn, Nb5Sn2Si, (Ti,Nb)6Sn5, and Nb5Ge3 were formed. After the oxidation at 1200 °C, the solid solution in the bulk of the alloy was very Ti-rich (Ti,Nb)ss. Improvement of oxidation resistance at both temperatures was accompanied by a decrease and increase, respectively, of the alloy parameters VEC (valence electron concentration) and δ, in agreement with the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration). The elimination of scale spallation at 1200 °C was attributed (a) to the formation of Ti-rich (Ti,Nb)ss solid solution and (Ti,Nb)6Sn5, respectively, in the bulk and below the scale, (b) to the low concentration of Cr in the scale, (c) to the absence of GeO2 in the scale, (d) to the formation of αAl2O3 in the scale, and (e) to the presence (i) of Nb5Ge3 below the scale/substrate interface and (ii) of oxides in the scale, namely, SiO2, Al2O3, TiO2, and SnO2, and Ti2Nb10O29,TiNb2O7, and AlNbO4, respectively, with a range of intrinsic thermal shock resistances and coefficient of thermal expansion (CTE) values that reduced stresses in the scale and the substrate below it.

The Microstructures and Hardness Analysis of a New Hypereutectoid Mn-Cr-Mo-V Steel

2013 ◽  
Vol 58 (2) ◽  
pp. 563-568
Author(s):  
R. Dabrowski ◽  
E. Rozniata ◽  
R. Dziurka
Keyword(s):  
Heat Treatment ◽  
Chemical Composition ◽  
Liquid Nitrogen ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Chemical Compositions ◽  
Tool Steels ◽  
Maximum Hardness ◽  
Hypereutectoid Steel ◽  
Tempering Temperature

The results of a microstructure and hardness investigations of a new hypereutectoid Mn-Cr-Mo-V steel, imitating by its chemical composition tool steels, are presented in the paper. The microstructure as well hardness changes, caused by austenitising and tempering temperatures were assessed, for samples quenched and sub-quenched in liquid nitrogen, directly after the quenching treatment. Additionally, the influence of the tempering temperature on the volume fraction of the retained austenite was estimated. New hypereutectoid steel, after an appropriate heat treatment obtained the relevant hardness of the tools used in the cold and hot working proces. It was indicated that the steel hardness increases with the increases of the austenitising temperature. At 800ºC the hardness of the quenched samples were equal 895HV, and for the sub-quenched samples 937HV. The maximum hardness, after tempering (746HV), was found at a temperature of 520ºC. It will be possible, in future, to apply this obtained investigation results in designing chemical compositions and microstructures of the new hypereutectoid alloyed steels of properties required by their users.

The Influence of Ni on the Microstructure of Co-Base ODS Alloys

2012 ◽  
Vol 535-537 ◽  
pp. 1011-1014 ◽  
Author(s):  
Lin Zhang ◽  
Xin Bo He ◽  
Ming Li Qin ◽  
Ye Liu ◽  
Xuan Hui Qu
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Mechanical Alloying ◽  
Cleavage Fracture ◽  
Fracture Strength ◽  
Volume Fraction ◽  
Secondary Phases ◽  
The Matrix ◽  
Ods Alloys ◽  
Low Volume

Co-based ODS alloys strengthened by γ΄ precipitates and nanosized oxides are promising high-temperature structural materials. Single solid solution of Al and W in the matrix can not be achieved after mechanical alloying, resulting in the formation of low volume fraction of γ΄ phase and several kinds of secondary phases. The addition of Ni promotes the precipitation of γ΄ phase and reduces the amount of secondary phases by the enlargement of the solid solution limit of Al and W within the matrix. In comparison with the lower fracture strength and cleavage fracture mode of the alloy without the addition of Ni, Ni-containing Co-base ODS alloys exhibit much higher fracture strength and obvious ductile facture mode.

scholarly journals On the Microstructure and Properties of Nb-12Ti-18Si-6Ta-2.5W-1Hf (at.%) Silicide-Based Alloys with Ge and Sn Additions

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1778 ◽  
Author(s):  
Jiang Zhao ◽  
Claire Utton ◽  
Panos Tsakiropoulos
Keyword(s):  
Experimental Data ◽  
Chemical Composition ◽  
Oxidation Kinetics ◽  
Design Methodology ◽  
Oxidation Behavior ◽  
Primary Phase ◽  
Specific Research ◽  
Parabolic Oxidation ◽  
Parameter Values ◽  
Better Than

In this paper two Nb-silicide-based alloys with nominal compositions (at.%) Nb-12Ti-18Si-6Ta-2.5W-1Hf-2Sn-2Ge (JZ1) and Nb-12Ti-18Si-6Ta-2.5W-1Hf-5Sn-5Ge (JZ2) were studied. The alloys were designed using the alloy design methodology NICE to meet specific research objectives. The cast microstructures of both alloys were sensitive to solidification conditions. There was macro-segregation of Si in JZ1 and JZ2. In both alloys the βNb5Si3 was the primary phase and the Nbss was stable. The A15-Nb3X (X = Ge,Si,Sn) was stable only in JZ2. The Nbss+βNb5Si3 eutectic in both alloys was not stable as was the Nb3Si silicide that formed only in JZ1. At 800 °C both alloys followed linear oxidation kinetics and were vulnerable to pesting. At 1200 °C both alloys exhibited parabolic oxidation kinetics in the early stages and linear kinetics at longer times. The adhesion of the scale that formed on JZ2 at 1200 °C and consisted of Nb and Ti-rich oxides, silica and HfO2 was better than that of JZ1. The microstructure of JZ2 was contaminated by oxygen to a depth of about 200 μm. There was no Ge or Sn present in the scale. The substrate below the scale was richer in Ge and Sn where the NbGe2, Nb5(Si1-xGex)3, W-rich Nb5(Si1-xGex)3, and A15-Nb3X compounds (X = Ge,Si,Sn) were formed in JZ2. The better oxidation behavior of JZ2 compared with JZ1 correlated well with the decrease in VEC and increase in δ parameter values, in agreement with NICE. For both alloys the experimental data for Si macrosegregation, vol.% Nbss, chemical composition of Nbss and Nb5Si3, and weight gains at 800 and 1200 °C was compared with the calculations (predictions) of NICE. The agreement was very good. The calculated creep rates of both alloys at 1200 °C and 170 MPa were lower than that of the Ni-based superalloy CMSX-4 for the same conditions but higher than 10−7 s−1.

Diffusion in MC Carbides in High-Speed Steels during High-Temperature Treatments

2010 ◽  
Vol 297-301 ◽  
pp. 1065-1070 ◽  
Author(s):  
Alexander S. Chaus ◽  
Matej Beznák
Keyword(s):  
Heat Treatment ◽  
High Temperature ◽  
Chemical Composition ◽  
High Speed ◽  
Diffusion Processes ◽  
Volume Fraction ◽  
High Speed Steel ◽  
Final Heat Treatment ◽  
Quenching And Tempering ◽  
Strong Diffusion

The microstructure and chemical composition of MC carbides in the modified variants of AISI M2 type high-speed steel after casting, annealing, carburising and subsequent final heat treatment (quenching and tempering) have been studied by focusing on diffusion processes in these carbides and their stability during high-temperature treatments. Significant changes in both the microstructure and chemical composition of the MC carbides as well as in their volume fraction shown to occur in the high-speed steels studied were attributed to decomposition, coagulation and dissolution of these carbides during heat treatments caused by strong diffusion of alloying elements and carbon. It was also shown that boron, in general, strongly suppressed the diffusion of carbon during carburising.

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.

Sign in / Sign up

Export Citation Format

Share Document