真空感应熔炼Nb-16Si-22Ti-2Hf-2Cr-2Al合金的组织和性能

The melt with a nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was poured in a ceramic shell mould with a temperature gradient of about 4℃/mm, and the ingot with the dimension of 60 mm×170 mm was obtained. The relationship between the microstructure and mechanical properties was measured, and the effects of the silicide on fracture toughness at ambient temperature and compression strength at high temperature were analyzed. It is revealed that the microstructure of the alloy consists of Nb solid solution and silicides, and the cooling rate can obviously change primary phase and constituent phases. The volume fraction of Nb₃Si formed at rapid cooling rate is significantly increased, and Nb₅Si₃ phase is formed with decreasing in cooling rate, whereas the volume fraction of the eutectic colonies and Nb_SS dendrites increase evidently, especially the second dendrite arm. Fine and uniform eutectic colonies are contributed to the ambient tensile strength, while the coarse primary Nb₃Si decreases the tensile strength but improves the compression strength of the alloy. When the microstructure is mainly composed of fine (Nb_SS+Nb₅Si₃) eutectic colonies, the tensile strength and elongation of the alloy reach 449 MPa and 0.3%, respectively. When lath-like Nb₃Si phase has 80 $\mu$m in width and 50% in volume fraction as well as its long axis is parallel to compression direction, the compression strength of the alloy at 1250℃ is about 650 MPa.     

定向凝固对Nb-14Si-22Ti-2Hf-2Al-4Cr合金组织和高低温力学性能的影响

采用光悬浮炉在氩气环境下制备了成分为Nb-14Si-22Ti-2Hf-2Al-4Cr的定向凝固试棒,研究了凝固工艺对合金相组成、组织形貌和高低温力学性能的影响,并与电弧熔炼态的合金进行了比较。结果表明,定向凝固试样相组成与电弧熔炼态相比没有发生变化,均由Nb基固溶体(Nb solid solution, NbSS)和Nb/Si化合物Nb5Si3组成,定向凝固合金NbSS呈枝晶状,硅化物呈板条状沿着生长方向分布。与电弧熔炼态相比,定向凝固速度为15和10 mm/h的合金在1250 ℃的抗压缩强度从电弧熔炼态的290 MPa分别提高到约442和493 MPa;15 mm/h的定向凝固后,合金的室温断裂韧性从电弧熔炼态的12 MPa·m1/2增加到15 MPa·m1/2。通过光悬浮定向凝固法制备的该合金具有优良的高低温力学性能     

球磨时间和热压温度对粉末冶金Nb-16Si-22Ti-2Al-2Hf-2Cr合金显微组织和室温力学性能的影响

采用粉末冶金法制备了Nb-16Si-22Ti-2Al-2Hf-2Cr合金,研究了粉末球磨时间(5、10、20h)及热压烧结温度(1500、1600℃)对合金组织和室温力学性能的影响。结果表明:热压烧结后的合金由Nb基固溶体NbSS、Ti基固溶体TiSS和硅化物Nb5Si3三相组成。随着球磨时间的延长,Nb5Si3和TiSS的含量增加,而NbSS的含量减少。室温硬度随球磨时间延长和热压烧结温度的升高而提高,20h/1600℃热压烧结合金硬度值最高,HV硬度达到11500MPa。1500和1600℃热压烧结下合金的断裂韧性随着粉末球磨时间的延长均呈下降的趋势,5h/1500℃热压烧结合金断裂韧性值最高,为10.14MPa·m1/2。     

球磨时间和热压温度对粉末冶金Nb-16Si-22Ti-2Al-2Hf-2Cr合金显微组织和室温力学性能的影响

采用粉末冶金法制备了Nb-16Si-22Ti-2Al-2Hf-2Cr合金,研究了粉末球磨时间（5、10、20 h）及热压烧结温度（1500、1600 ℃）对合金组织和室温力学性能的影响。结果表明：热压烧结后的合金由Nb基固溶体NbSS、Ti基固溶体TiSS和硅化物Nb5Si3三相组成。随着球磨时间的延长,Nb5Si3和TiSS的含量增加,而NbSS的含量减少。室温硬度随球磨时间延长和热压烧结温度的升高而提高,20 h/1600 ℃热压烧结合金硬度值最高,HV硬度达到11500 MPa。1500和1600 ℃热压烧结下合金的断裂韧性随着粉末球磨时间的延长均呈下降的趋势,5 h/1500 ℃热压烧结合金断裂韧性值最高,为10.14 MPa·m1/2。     

Nb-16Si-22Ti-2Cr-2Al-2Hf-xFe合金热加工性能研究

通过对真空非自耗电弧炉制备的Nb-16Si-22Ti-2Cr-2Al-2Hf-xFe(x=0, 1,2, 3, 5, at%) 5种铌硅合金的热变形行为进行探索和研究,分别绘制了5种铌硅合金的热加工图,并分析了不同变形参数下合金显微组织的变化,确定了各合金的最佳变形工艺范围,为后续铌硅合金的设计及热加工研究提供了理论依据。合金耗散效率因子η的最大值出现在低应变速率及高温区域;最小值则出现在低温和高应变速率区域。不同Fe含量合金的热加工图中均存在失稳变形区,主要分布区域与低耗散效率因子区重合,同时,失稳区晶粒明显拉长,晶界出现弯曲扭折现象,晶粒大小分布不均匀,发生了局部塑性流动。稳定变形区存在链状的动态再结晶组织,细小的再结晶晶粒沿晶界分布,随着变形温度的升高和应变速率的降低,动态再结晶晶粒的尺寸增大。     

Ti-25Al-14Nb-2Mo-1Fe合金高温力学性能研究

通过加入第四组元β相稳定元素Fe和Mo来替代部分Nb元素制备Ti-25Al-14Nb-2Mo-1Fe合金.结果表明,较参比材料Ti-22Al-27Nb合金,Ti-25Al-14Nb-2Mo-1Fe合金的瞬时蠕变应变、1％蠕变时间和稳态蠕变速率均得到较大改善,并且自扩散激活能也得到提高;该合金在650℃高温条件下,具有较好的力学性能.     

Ti对Nb-20Si-5Al超高温合金性能的影响

采用放电等离子烧结法(SPS)制备了Nb-20Si-5Al-xTi(x=0,18,20,22,摩尔分数)超高温合金,研究了Ti加入量对Nb-20Si-5Al合金的室温断裂韧度和高温抗氧化性的影响。结果表明,随着Ti加入量的增加,超高温合金的相组成由Nbss、Nb₅Si₃和Al3Nb相转变成为Nbss、(Nb,Ti)5Si3和Ti相。Ti能明显改善Nb-20Si-5Al超高温合金的断裂韧度和高温抗氧化性能,随着Ti加入量的增加均先提高然后降低,在Ti加入量为20%时,合金断裂韧度最大,为7.41 MPa·m^1/2,相比未加Ti时提高了约56.9%,其高温氧化速率最低,为0.72×10^-4g²/(cm⁴·h)。添加Ti元素后,其氧化产物中出现Ti₂Nb₁₀O₂₉、TiNb₂O₇、TiO₂等,可以提高其氧化膜的致密性,从而提高高温抗氧化性能。     

粉末冶金Nb-35Ti-6Al-5Cr-8V合金组织演变及其力学行为

采用粉末冶金法对不同球磨时间的Nb-35Ti-6Al-5Cr-8V合金机械合金化粉末塑变行为,热压烧结材料的微观组织结构和力学行为进行了研究。研究结果表明：塑性良好的Nb-35Ti-6Al-5Cr-8V粉末随着球磨时间增加首先变形为大尺寸的片状、后经持续的加工硬化破碎成絮状;热压烧结能够制备微观组织可控晶粒细化的Nb-35Ti-6Al-5Cr-8V合金,合金由单一的Nbss相构成,Ti、Al、Cr、V元素固溶引起Nb晶格尺寸减小0.0685 ?;随着球磨时间增加合金晶粒明显细化进而显著提高了合金的维氏硬度和室温压缩强度,其变化符合材料硬度和强度的Hall-Petch规律。粉末冶金制备Nb-35Ti-6Al-5Cr-8V合金的各项力学性能明显优于熔铸法制备合金。     

热处理对Ti-3Al-5Mo-4Cr-2Zr-1Fe合金组织与力学性能的影响研究

对Ti-3Al-5Mo-4Cr-2Zr-1Fe(Ti-35421)合金进行了不同工艺的固溶时效处理,研究了热处理后的组织演变规律与力学性能。结果表明：经不同温度固溶+540℃时效后,随着固溶温度的升高,初生α相板条变短变粗,体积分数减少,针状次生α相体积分数增加,Ti-35421合金的强度增加,塑韧性减小,拉伸断口表面韧窝数量减少、尺寸变小,逐渐出现微孔和空洞;经775℃固溶+不同温度时效后,随着时效温度的升高,针状次生α相变短变粗,次生α相间距增大,合金的强度减小,塑韧性增加,拉伸断口表面韧窝逐渐变大变深,微孔和空洞逐渐消失。当热处理工艺为775℃/1 h/AC+560℃/16 h/AC时,Ti-35421合金的抗拉强度为1125 MPa,屈服强度为1024 MPa,延伸率为5.5%,冲击吸收功为36.3 J,具有良好的强塑韧性匹配。     

Ti-48Al-2Cr-2Nb-( TiB2, Ni)合金凝固组织演变规律及力学性能研究

TiAl合金已成为航空航天工程升级换代的关键材料,然而其铸态晶粒尺寸粗大,室温塑性和强度低,限制其进一步工程应用。本文采用真空感应凝壳熔炼工艺系制备铸锭,系统研究TiB2和Ni元素共同添加对Ti-48Al-2Cr-2Nb合金凝固组织和力学性能的影响。结果表明,TiB2及Ni合金化后,合金的凝固路径和初生相并未改变,晶粒尺寸从700μm细化至100μm,生成片状TiB2和富镍τ3相。T4822-( Ni, TiB2)合金的室温拉伸强度与基体合金相近,断裂伸长率提高30%。700-900℃时,T4822-(Ni, TiB2)合金的抗拉强度始终高于基体合金,在900℃时抗拉强度达到365MPa,较基体合金提高9%。800℃和900℃时T4822-(Ni, TiB2)合金的断裂伸长率分别达到25.3%和36.1%,远高于基体合金。晶粒尺寸的细化和晶界处的块状γ相是T4822-(Ni, TiB2)合金塑性提升的主要原因,其良好的高温强度则可以归因于片层团内部和界面处的硬质硼化物和富镍τ3相。     

真空烧结温度对Ti-44Al-2Cr-4Nb-0.2W-0.2B合金显微组织及力学性能的影响

为获得细晶TiAl合金及有效减少传统铸造带来的内部缺陷,采用真空热压烧结工艺制备了Ti-44Al-2Cr-4Nb-0.2W-0.2B合金,研究了烧结温度对TiAl合金微观组织及力学性能的影响。结果表明:Ti、Al元素粉末反应合成后,经XRD检测,3种烧结温度(1150、1240、1300℃)烧结后的合金主要由γ-TiAl和α_2-Ti_3Al_2种基体相组成,随着烧结温度的增加,γ相含量增加,α_2相则减少;结合SEM观察发现,改变烧结温度可获得TiAl合金不同典型组织,其中1150℃烧结合金为近γ组织、1240℃烧结为双态组织、1300℃烧结为近片层组织,烧结温度的升高使得合金组织愈发均匀;配合EDS分析,烧结温度的升高有助于Nb元素在基体相中的扩散,同时合金密度随烧结温度的升高逐步增大,当烧结温度升至1300℃,合金的密度达到4.419g/cm~3;通过力学性能检测,在1240℃烧结制备的TiAl合金组织为细小的双态组织,显示出较好的综合力学性能,其显微硬度为5270 MPa,在高温压缩时展示出良好的抗压强度。     

Effects of Zr Content on the Microstructures and Tensile Properties of Ti-3Al-8V-6Cr-4Mo-xZr Alloys

The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-xZr(x = 0,2,4 and 6) titanium alloys were investigated.The precipitated phases and tensile fracture morphologies were observed using scanning electron microscopy and transmission electron microscopy.Experimental results show that the presence of trace impurity Si and the addition of Zr induce the formation of(TiZr)_6Si_3 silicides.The quantity of silicides increases with Zr content increasing.The dispersed silicides refined the grain size of β Zr-containing alloys,and the grain size decreases significantly with Zr content increasing.Accompanying these microstructural changes,the strength of the alloys is enhanced gradually with the increase of Zr content,which is attributed to the combination of precipitation strengthening and grain refinement.     

The microstructure evolution of directionally solidified Nb-22Ti-14Si-4Cr-2Al-2Hf alloy during heat treatment

To obtain a homogenous and optimizing microstructure, non-equilibrium directionally solidified (DS) samples at high withdrawal rate were heat treated (HT). The heat treatments were carried out at 1500 °C for 3–100 h. The DS and HT samples consisted of Nb_SS, α-Nb₅Si₃ and γ-Nb₅Si₃, and the DS morphology altered significantly after heat treatment. The well developed Nb_SS dendrites were compromised and the size decreased from more than 100 μm to less than 60 μm when the heat treated time was 6 h. On the other hand, the Nb_SS in eutectic interconnected and meanwhile connected with the dendrites, and the frequency of small size got lower with the heat treated time increasing. When heat treated for 100 h, the size of Nb_SS was comparatively uniform and concentrate in the region of 5–20 μm with a value of 63% for Ostwald ripening. The dendric and eutectic morphologies exited in the DS sample disappeared, turning into a net-work structure. The components of primary Nbss dendrites and Nbss in the intercellular regions were homogenized after heat treated for 3 h. However the enrichment of Ti, Cr and Hf in γ-Nb₅Si₃ compared to α-Nb₅Si₃ could not be eliminated by homogenizing treatment even for 100 h.     

退火温度对Ti-6Al-3Nb-2Zr-1Mo合金组织及力学性能的影响

研究了退火温度对Ti-6Al-3Nb-2Zr-1Mo合金组织和力学性能的影响。结果表明:随着退火温度升高,初生α相含量降低,2°～15°小角度晶界逐渐减少;退火温度较高时,退火过程中发生了α相→β相→α相的相变,<0001>//横向织构消失。随着退火温度升高,Ti-6Al-3Nb-2Zr-1Mo合金屈服强度逐渐降低,抗拉强度、延伸率先升高后降低。退火温度升高后,片层组织比例升高,裂纹扩展功占冲击吸收功的比例增大,材料韧性提升。     

时效处理对Ti-6Al-3Nb-2Zr-Mo合金组织演变和力学性能的影响

为了解不同时效参数对Ti-6Al-3Nb-2Zr-Mo(Ti6321)合金组织和力学性能影响的根本原因,通过光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和力学性能测试,研究了不同时效条件(500～650℃,3～24 h)下的显微组织和力学性能。结果表明,次生相α(α_s)比初生相α(α_p)对时效参数更为敏感。此外,α_s相的厚度与时效温度和时效时间呈正相关。随着时效温度和时效时间的增加,Ti和Al元素在β_t相中的偏析明显,α_s相由细针状转变为长棒状。当合金在600℃时效12 h时,合金表现出较好的综合力学性能。抗拉伸强度、屈服强度和伸长率分别为907 MPa、796 MPa和16%,冲击功为55 J。