To investigate the effect of solidification parameters on the solidification path and microstructure evolution of Ti-45Al-5Nb(at.%) alloy, Bridgman-type directional solidification and thermodynamics calculations were ...To investigate the effect of solidification parameters on the solidification path and microstructure evolution of Ti-45Al-5Nb(at.%) alloy, Bridgman-type directional solidification and thermodynamics calculations were performed on the alloy. The microstructures, micro-segregation and solidification path were investigated.The results show that the β phase is the primary phase of the alloy at growth rates of 5-20 μm·s^(-1) under the temperature gradients of 15-20 K·mm^(-1), and the primary phase is transformed into an α phase at relatively higher growth rates(V >20 μm·s^(-1)). The mainly S-segregation and β-segregation can be observed in Ti-45Al-5Nb alloy at a growth rate of 10 μm·s^(-1) under a temperature gradient of 15 K·mm^(-1). The increase of temperature gradient to 20 K·mm^(-1) can eliminate β-segregation, but has no obvious effect on S-segregation. The results also show that 5 at.% Nb addition can expand the β phase region, increase the melting point of the alloy and induce the solidification path to become complicated. The equilibrium solidification path of Ti-45Al-5Nb alloy can be described as L L→β L+β L+β→αα+β_R β→ααα→γα+γα→α_2+γγ_R+(α_2+γ), in which β_R and γ_R mean the residual β and展开更多
Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendri...Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendritic coherency solid fraction have been studied by double-thermocouple thermal analysis.The solidification contraction stress vs.temperature(and time)curves are measured by using a“T”type hot tearing permanent-mold.The results reveal that the CSC^(∗)prediction values are in good agreement with the experimental results.Moreover,Al_(2)Y phase acts as the heterogeneous nucleation core ofα-Mg and significantly influences the grain size.It has been observed that minimum grain size,optimal dendritic coherency and minimum HTS are exhibited by Mg-2Zn-(3+0.5 x)Y-x Al alloy(x=2).Furthermore,when Al content was increased to 3 at%,Al_(2)Y phase exhibited a peritectic reaction and transformed into a mixed structure of Al_(2)Y and Al+Al_(3)Y phases,which increased the HTS of the alloy due to reduced fine-grained Al_(2)Y content.展开更多
Abstract The as-cast microstructures and solidification paths of the Nb-Si-Ti ternary alloys in the NbsSi3-TisSi3 region were investigated. Since there exist some isomor- phous compounds in the NbsSi3-TisSi3 region, s...Abstract The as-cast microstructures and solidification paths of the Nb-Si-Ti ternary alloys in the NbsSi3-TisSi3 region were investigated. Since there exist some isomor- phous compounds in the NbsSi3-TisSi3 region, such as aNbsSi3 with B3Cr5 prototype, 13NbsSi3 with Si3W5 pro- totype, 7NbsSi3 with MnsSi3 prototype, and TisSi3 with MnsSi3 prototype, the primary solidification areas of these compounds were not typically indentified in previous experiments. In the present paper, the microstructure observation, the phase identification, and the composition measurement were performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA), respectively. No ternary compound is found. There exist three primary solidification areas, 13Nbs_x(Ti)xSi3, ~Nbs_x(Ti)xSi3, and Tis-x(Nb)xSi3 in the NbsSi3-TisSi3 region. Together with the literaturereported experimental data and optimization results, the liquidus projection of the whole Nb-Si-Ti ternary system is constructed, and totally ten primary solidification areas-- diamond-Si, Nb1-x(Ti)xSi2, Ti1-x(Nb)xSi2, Ti1-x(Nb)xSi, Ti5-x(Nb)xSi4, βNb5-x(Ti)xSi3,αNb5-x(Ti)xSi3, Ti5-x (Nb)xSi3, (Nb,Ti)3Si, and BCC--and nine transitional invariant reactions-L + Nb1-x(Ti)xSi2 → Ti1-x(Nb)x Si2 + Si, L + Nb1-x(Ti)xSi2 → Ti1-x(Nb)xSi2 + Ti5- (Nb)xSi4, L + Ti5-x(Nb)xSi4 → Ti1-x(Nb)xSi2 + Ti1-x (Nb)xSi, L + 13Nb5-x(Ti)5Si3→ Nb1-x(Ti)xSi2 + Ti5-x (Nb)xSi4, L + βNb5-x(Ti)xSi3→b5-x(Ti)xSi3 +Ti5-x (Nb)xSi4, L + αNb5-x(Ti)αSi3 → Ti5-x(Nb)xSi3 + Ti5-x(Nb)x Si4, L + αNb5-x(Ti)xSi3 →βNb5-x(Ti)xSi3 + Ti5-x(Nb)xSi3, L + βNb5-xTb-xSi3 → Ti5-x(Nb)xSi3 + (Nb,Ti)3Si, and L + (Nb,Ti)3Si → Ti5-x(Nb)xSi3 + BCC are confirmed.展开更多
The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical ...The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the eff ects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-MgSi, Q-phase and θ-AlCu, the hot cracking phenomenon and mechanical properties are eff ectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of(6.4 ± 0.4)% and hardness of 162 ± 2(HV) at the laser energy density of 112.5 J/mm~3. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.展开更多
To improve the microstructure and microhardness,Ti-48Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.The microstructure and microhardness of rapidly solidified Ti-48Al alloy were sy...To improve the microstructure and microhardness,Ti-48Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.The microstructure and microhardness of rapidly solidified Ti-48Al alloy were systematically investigated.Results show that the average lamellar colony size of the alloy reduces from 60.6μm to 11μm as the cooling rate increases from 2.3×105 to 5.1×105 K·s-1,caused by the increase of nucleation rate at a higher cooling rate.At the high cooling rate of(4.3-5.1)×105 K·s-1,theαphase is the primary phase,and a few metastableαphases are reserved,which then transform intoα2 phase and subsequently lead to the formation ofα2 equiaxed grain.The lamellar spacing also decreases with the increase of cooling rate.The relationship between lamellar spacing(d)and cooling rate(v)is d=33.6v-1.34.The microhardness increases with the increase of cooling rate because the refined lamellar spacing and grain size can improve the microhardness.展开更多
Ruthenium(Ru)is a promising element to heighten the comprehensive mechanical properties of TiAl alloys.In the present study,the phase transformation during the cooling of Ti-47Al-2Cr-2Nb-xRu(x=0,0.1,0.5,1.0,at.%)alloy...Ruthenium(Ru)is a promising element to heighten the comprehensive mechanical properties of TiAl alloys.In the present study,the phase transformation during the cooling of Ti-47Al-2Cr-2Nb-xRu(x=0,0.1,0.5,1.0,at.%)alloys was investigated.The results show that Ru tends to segregate in the interdendritic region during solidification,and therefore,refines the as-cast microstructure of the alloys.As aβ-stabilizer,Ru does not induce a novel solidification reaction but maintains the peritectic reaction of L+β→α.An excessive Ru content would cause the formation of(γ+τ1+B2)and(α+γ+τ1+B2)phase regions below 1,250°C.The precipitation ofτ1-containing mixture is attributed to the Ru-segregation,which inhibits the reaction ofα→γand facilitates the formation of B2 phase.The discontinuous coarsening ofγphase and blockτ1 phase formed alternately in a manner of analogous eutectoid decomposition within B2 phase.In addition,the effect of Ru content on compression property of the alloys was studied.The yield strength increases up to 427 MPa at 800°C with the addition of 1.0at.%Ru,which is mainly due to the solution strengthening effect of Ru.展开更多
In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.Microstructure and microhardness of the...In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.Microstructure and microhardness of the alloy before and after rapid solidification were investigated.XRD results show that the ratio ofα2 phase in binary alloy increased with the cooling rates,which is caused by moreαphases directly transforming toα2 phases.Grain morphology changed from long dendrite to the mixture of equiaxed and dendrite to equiaxed with the increase of cooling rates.The grain size was refined from 200-600μm of as⁃cast to 18μm of the alloy cooled at 4.9×10^5 K/s,which is caused by the undercooling induced from rapid solidification.Lamellar spacing was decreased from 4.5μm of as⁃cast to 1.1μm by rapid solidification.With the increase of cooling rate,the content ofα2 phase increased andγphase decreased gradually.Rapid solidification can reduce the segregation of elements.The microhardness was improved from 247 HV to 556 HV,which results from grain refinement strengthening,reduction of lamellar spacing,and more content ofα2 phase.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.51331005 and 51425402)
文摘To investigate the effect of solidification parameters on the solidification path and microstructure evolution of Ti-45Al-5Nb(at.%) alloy, Bridgman-type directional solidification and thermodynamics calculations were performed on the alloy. The microstructures, micro-segregation and solidification path were investigated.The results show that the β phase is the primary phase of the alloy at growth rates of 5-20 μm·s^(-1) under the temperature gradients of 15-20 K·mm^(-1), and the primary phase is transformed into an α phase at relatively higher growth rates(V >20 μm·s^(-1)). The mainly S-segregation and β-segregation can be observed in Ti-45Al-5Nb alloy at a growth rate of 10 μm·s^(-1) under a temperature gradient of 15 K·mm^(-1). The increase of temperature gradient to 20 K·mm^(-1) can eliminate β-segregation, but has no obvious effect on S-segregation. The results also show that 5 at.% Nb addition can expand the β phase region, increase the melting point of the alloy and induce the solidification path to become complicated. The equilibrium solidification path of Ti-45Al-5Nb alloy can be described as L L→β L+β L+β→αα+β_R β→ααα→γα+γα→α_2+γγ_R+(α_2+γ), in which β_R and γ_R mean the residual β and
基金The authors would like to acknowledge the financial support from the National Natural Science Foundation of China(Nos.51571145 and 51504153)Innovation Talent Pro-gram in Sciences and Technologies for Young and Middle-aged Scientists of Shenyang(No.RC180111)+2 种基金Doctoral Scientific Research Foundation of Liaoning Province(No.20170520033)Youth Project of Liaoning Education Depart-ment(No.LQGD20170328)Natural Science Foundation of Liaoning Province(No.201602548).In addition,the authors would also like to thank Zhenglai Zhang from Zhejiang Hua Shuo Technology Co.,Ltd.and Ningbo City“Science and Technology Innovation 2025”major special project(new en-ergy vehicle lightweight magnesium alloy material precision forming technology research)funding support.
文摘Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendritic coherency solid fraction have been studied by double-thermocouple thermal analysis.The solidification contraction stress vs.temperature(and time)curves are measured by using a“T”type hot tearing permanent-mold.The results reveal that the CSC^(∗)prediction values are in good agreement with the experimental results.Moreover,Al_(2)Y phase acts as the heterogeneous nucleation core ofα-Mg and significantly influences the grain size.It has been observed that minimum grain size,optimal dendritic coherency and minimum HTS are exhibited by Mg-2Zn-(3+0.5 x)Y-x Al alloy(x=2).Furthermore,when Al content was increased to 3 at%,Al_(2)Y phase exhibited a peritectic reaction and transformed into a mixed structure of Al_(2)Y and Al+Al_(3)Y phases,which increased the HTS of the alloy due to reduced fine-grained Al_(2)Y content.
基金supported by the National Natural Science Foundation of China (No. 51271027)the National High Technology Research and Development Program of China (No. 2013AA031601)
文摘Abstract The as-cast microstructures and solidification paths of the Nb-Si-Ti ternary alloys in the NbsSi3-TisSi3 region were investigated. Since there exist some isomor- phous compounds in the NbsSi3-TisSi3 region, such as aNbsSi3 with B3Cr5 prototype, 13NbsSi3 with Si3W5 pro- totype, 7NbsSi3 with MnsSi3 prototype, and TisSi3 with MnsSi3 prototype, the primary solidification areas of these compounds were not typically indentified in previous experiments. In the present paper, the microstructure observation, the phase identification, and the composition measurement were performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA), respectively. No ternary compound is found. There exist three primary solidification areas, 13Nbs_x(Ti)xSi3, ~Nbs_x(Ti)xSi3, and Tis-x(Nb)xSi3 in the NbsSi3-TisSi3 region. Together with the literaturereported experimental data and optimization results, the liquidus projection of the whole Nb-Si-Ti ternary system is constructed, and totally ten primary solidification areas-- diamond-Si, Nb1-x(Ti)xSi2, Ti1-x(Nb)xSi2, Ti1-x(Nb)xSi, Ti5-x(Nb)xSi4, βNb5-x(Ti)xSi3,αNb5-x(Ti)xSi3, Ti5-x (Nb)xSi3, (Nb,Ti)3Si, and BCC--and nine transitional invariant reactions-L + Nb1-x(Ti)xSi2 → Ti1-x(Nb)x Si2 + Si, L + Nb1-x(Ti)xSi2 → Ti1-x(Nb)xSi2 + Ti5- (Nb)xSi4, L + Ti5-x(Nb)xSi4 → Ti1-x(Nb)xSi2 + Ti1-x (Nb)xSi, L + 13Nb5-x(Ti)5Si3→ Nb1-x(Ti)xSi2 + Ti5-x (Nb)xSi4, L + βNb5-x(Ti)xSi3→b5-x(Ti)xSi3 +Ti5-x (Nb)xSi4, L + αNb5-x(Ti)αSi3 → Ti5-x(Nb)xSi3 + Ti5-x(Nb)x Si4, L + αNb5-x(Ti)xSi3 →βNb5-x(Ti)xSi3 + Ti5-x(Nb)xSi3, L + βNb5-xTb-xSi3 → Ti5-x(Nb)xSi3 + (Nb,Ti)3Si, and L + (Nb,Ti)3Si → Ti5-x(Nb)xSi3 + BCC are confirmed.
基金financially supported by the Joint Fund Project of Equipment Pre-research of Education Ministry(Grant No.6141A02033230)。
文摘The construction and application of traditional high-strength 7075 aluminum alloy(Al7075) through selective laser melting(SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the eff ects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-MgSi, Q-phase and θ-AlCu, the hot cracking phenomenon and mechanical properties are eff ectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of(6.4 ± 0.4)% and hardness of 162 ± 2(HV) at the laser energy density of 112.5 J/mm~3. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.
基金the National Natural Science Foundation of China(Grant No.51825401)the China Postdoctoral Science Foundation(Grant No.2019TQ0076)the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(Grant No.2016ZT06G025)。
文摘To improve the microstructure and microhardness,Ti-48Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.The microstructure and microhardness of rapidly solidified Ti-48Al alloy were systematically investigated.Results show that the average lamellar colony size of the alloy reduces from 60.6μm to 11μm as the cooling rate increases from 2.3×105 to 5.1×105 K·s-1,caused by the increase of nucleation rate at a higher cooling rate.At the high cooling rate of(4.3-5.1)×105 K·s-1,theαphase is the primary phase,and a few metastableαphases are reserved,which then transform intoα2 phase and subsequently lead to the formation ofα2 equiaxed grain.The lamellar spacing also decreases with the increase of cooling rate.The relationship between lamellar spacing(d)and cooling rate(v)is d=33.6v-1.34.The microhardness increases with the increase of cooling rate because the refined lamellar spacing and grain size can improve the microhardness.
基金the financial support from the National Natural Science Foundation of China(No.51774238)the Open Project of Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education(No.LZUMMM2020008)+1 种基金the Natural Science Fundamental Research Foundation of Shaanxi Province(No.2020JM-086)the 2018 Joint Foundation of Ministry of Education for Equipment Pre-research(No.6141A020332)。
文摘Ruthenium(Ru)is a promising element to heighten the comprehensive mechanical properties of TiAl alloys.In the present study,the phase transformation during the cooling of Ti-47Al-2Cr-2Nb-xRu(x=0,0.1,0.5,1.0,at.%)alloys was investigated.The results show that Ru tends to segregate in the interdendritic region during solidification,and therefore,refines the as-cast microstructure of the alloys.As aβ-stabilizer,Ru does not induce a novel solidification reaction but maintains the peritectic reaction of L+β→α.An excessive Ru content would cause the formation of(γ+τ1+B2)and(α+γ+τ1+B2)phase regions below 1,250°C.The precipitation ofτ1-containing mixture is attributed to the Ru-segregation,which inhibits the reaction ofα→γand facilitates the formation of B2 phase.The discontinuous coarsening ofγphase and blockτ1 phase formed alternately in a manner of analogous eutectoid decomposition within B2 phase.In addition,the effect of Ru content on compression property of the alloys was studied.The yield strength increases up to 427 MPa at 800°C with the addition of 1.0at.%Ru,which is mainly due to the solution strengthening effect of Ru.
基金National Natural Science Foundation of China(Grant No.51825401)the China Postdoctoral Science Foundation(Grant No.2019TQ0077).
文摘In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.Microstructure and microhardness of the alloy before and after rapid solidification were investigated.XRD results show that the ratio ofα2 phase in binary alloy increased with the cooling rates,which is caused by moreαphases directly transforming toα2 phases.Grain morphology changed from long dendrite to the mixture of equiaxed and dendrite to equiaxed with the increase of cooling rates.The grain size was refined from 200-600μm of as⁃cast to 18μm of the alloy cooled at 4.9×10^5 K/s,which is caused by the undercooling induced from rapid solidification.Lamellar spacing was decreased from 4.5μm of as⁃cast to 1.1μm by rapid solidification.With the increase of cooling rate,the content ofα2 phase increased andγphase decreased gradually.Rapid solidification can reduce the segregation of elements.The microhardness was improved from 247 HV to 556 HV,which results from grain refinement strengthening,reduction of lamellar spacing,and more content ofα2 phase.