热暴露对Ti-44Al-4Nb-4Zr-0.2Si-1B合金显微结构及力学性能的影响

采用扫描电镜、透射电镜以及拉伸和高周疲劳等试验手段研究10 000 h、700℃大气热暴露过程对Ti-44Al-4Nb-4Zr-0.2Si- 1B合金显微结构和力学性能的影响.结果表明:复合含Nb-Zr的TiAl合金的α2+γ层片组织显示出较高的热力学稳定性,合金的α2+γ层片晶团在热暴露过程中,α2→γ和α2+γ→B...     

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.     

热处理对Ti-18Nb-10Zr合金微观组织和超弹性的影响

研究了固溶、固溶时效、短时退火对Ti-18Nb-10Zr(at%)合金微观组织和超弹性的影响。采用室温拉伸测试了合金超弹性;借助X射线衍射（XRD）、电子背散射衍射（EBSD）、透射电子显微镜（TEM）对微观组织、相变行为进行了观察与分析。结果表明,冷轧态Ti-18Nb-10Zr合金,800 ℃固溶后,发生了完全再结晶,由β相和细小的无热ω相组成,回复应变约为2.65%;再在350 ℃时效后,由于等温ω相尺寸和体积分数显著增加,急剧降低了合金Ms,应力-应变曲线未呈现超弹性;650 ℃短时退火后,合金基本完成再结晶,由单一的β相组成,平均晶粒尺寸约为10 μm,晶粒细化改善了合金超弹性,回复应变约为2.86%。     

船用Ti-6Al-3Nb-2Zr合金的微弧氧化陶瓷膜

采用微弧氧化技术,在磷酸盐溶液体系中在船用Ti-6Al-3Nb-2Zr合金表面制备陶瓷膜层.利用扫描电镜、光学显微镜、X射线衍射仪和显微硬度计对陶瓷膜的表面和截面形貌、氧化层厚度、相结构以及显微硬度进行观察测试,用电子万能材料试验机和数字万用表研究膜层的结合强度和绝缘性,并用MMS-1G高温高速销盘摩擦磨损试验机和YWX/Q-750盐雾试验机考察膜层的摩擦学性能和腐蚀性能.结果表明:膜层厚度可达到20 μm以上,陶瓷膜主要由金红石TiO2相和锐钛矿TiO2相构成,膜层与基体的结合强度达到30 MPa以上,膜层绝缘性和耐蚀性良好,耐磨性得到明显改善,膜层的磨损机制表现为轻微的磨粒磨损与粘着磨损,且以磨粒磨损为主.     

Ti-47Al—6Nb-2Cr合金的制备与表征

采用非自耗电弧熔炼铸造方法,制备了Ti-47Al-6Nb-2Cr合金。采用金相观察、扫描电镜及透射电镜对其显微组织进行表征。结果表明,Ti-47Al-6Nb-2Cr合金在双相区近γ处理加循环快速热处理,可有效地将粗大的柱状组织细化成50μm~100μm的层状组织,这一细化过程主要是利用了块型转变的逆反应γ→α转变。     

热处理对Nb-35Ti-4C合金微观组织和力学行为的影响

采用XRD、SEM和XRD对Nb-35Ti-4C合金热处理前后的相组成、界面结构、组织演变及力学行为进行研究。结果表明:热处理前后合金均由Nbss和(Nb,Ti)C构成。热处理过程中Nbss内部析出长条状的二次(Nb,Ti)C;(Nb,Ti)C内则析出长条状的二次Nbss。二次Nbss依附于fcc(Nb,Ti)C的密排面(111)面形核,与母相(Nb,Ti)C满足(N-W)位相关系:[011]_((Nb,Ti)C)//[001]_(Nbss), (111)_((Nb,Ti)C)//(110)_(Nbss)。碳化物与Nbss具有洁净良好的界面结合。热处理后单相(Nb,Ti)C变为(Nb,Ti)C+二次Nbss的共析组织。纳米压痕测试表明共析组织转变降低了碳化物的脆性,提高了合金的韧性。     

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     

Ti-42.85Al-12.3Nb-2Cr合金相组成对高温抗氧化性能的影响

通过热处理获得了合金Ti-42.85Al-12.3Nb-2Cr铸态(As-cast)、炉冷(FC)和水淬(WQ)3种含不同组成相和微观组织的合金,研究了这3种合金在1000℃静止空气中的断续氧化行为,采用XRD、SEM和EPMA分析了氧化膜的结构和组成.研究表明,Nb的加入能够显著提高合金的抗氧化性,但是高含量Nb的加入导致高温亚稳β相在室温组织中残留,β相使外层氧化膜的粘附性变差,促使氧化膜整体剥落.通过热处理消除β相后,获得的以γ α2为主相的炉冷合金中形成了有效的保护性氧化膜.     

High-Temperature Oxidation of Ti-48Al-2Nb-2Cr and Ti-25Al-10Nb-3V-1Mo

The short-term oxidation behavior of a-TiAl alloy (Ti-48Al-2Nb-2Cr) was compared andcontrasted to that of an₂-Ti₃Al base(Ti-25Al-19Nb-3V 1Mo) alloy. Oxidation ofTi-25Al-10Nb-3V-1Mo was found to occur at a moderate rate at 800°C, in aN₂ + 20% O₂ environment. A largeincrease in the oxidation rate occurred above thistemperature. This large weight increase was attributedto a breakdown in the protective oxide scale on the surface of the₂ intermetallic alloy, therebypermitting rapid diffusion of oxygen and nitrogen to thesurface of the intermetallic. The oxidation rate of thisalloy at 1200°C was not significantly higher thanthe oxidation rate at 1000°C. In contrast, theoxidation rate of Ti-48Al-2Nb-2Cr remained low up to1200°C. At this temperature, a significant increasein oxidation was observed and was attributed to acceleratedoxygen diffusion through the ₂ phaseand increased solubility of oxygen in the gamma phase ofthe intermetallic microstructure. This weight increaseoccurred despite the fact that at 1200°C, theintegrity of the oxide layer formed on the surface ofthis alloy was maintained. The results of this studyillustrate the need for developing protectiveenvironmental coatings tailored to the individualintermetallic alloy.     

EBSD characterization of recrystallization microstructure of cold-swaged Ti-23Nb-0.7Ta-2Zr-O alloy

The microstructures of the cold-swaged and recrystallized Ti-23Nb-0.7Ta-2Zr-O （TNTZO） （mole fraction, %） alloy were investigated by electron backscatter diffraction （EBSD）. The difference in microstructure, texture and recrystallization process was evaluated between the TNTZO alloy and traditional body centered cubic （bcc） metals. The results show that the cold-swaged TNTZO alloy presents a pronounced （110） fiber texture in the axial direction. The recrystallization of the TNTZO alloy is achieved by the nucleation of new grains and the growth of these new grains at the expense of the deformed structure. The TNTZO alloy behaves a very similar way to traditional bcc metals in the features of the microstructure, texture and recrystallization.     

Effect of enamel coating on oxidation and hot corrosion behaviors of Ti-24Al-14Nb-3V alloy

The effect of enamel coating on the isothermal and cyclic oxidation at 900 °C in air and on the hot corrosion resistance of Ti-24Al-14Nb-3V in both 85% Na₂SO₄+15%K₂SO₄ and 15%NaCl+85% Na₂SO₄ molten mixed salts at 850 °C was investigated. The results indicated that Ti-24Al-14Nb-3V alloy exhibited poor oxidation resistance due to the formation of nonprotective Al₂O₃+TiO₂+AlNbO₄ scales and poor hot corrosion resistance due to the spallation of scales formed in molten Na₂SO₄+K₂SO₄ and NaCl+Na₂SO₄. Enamel coating suppressed the migration of oxygen and corrosive ions into the substrate to improve the oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V alloy. However, the dissolution of oxides components of the coating into the molten salts degraded enamel coating and the degradation of the coating involved a process by which Cl⁻ anion penetrated into the substrate through voids in the coating to accelerate corrosion of Ti-24Al-14Nb-3V alloy.     

热机械处理对Ti-45Al-5Nb-0.3Y合金的显微组织与力学性能的影响

包套锻造Ti-45Al-5Nb-0.3Y合金由大量细小的动态再结晶等轴γ晶粒(晶粒尺寸可达1-2 μm),弯曲或破碎的层片和少量的残余平直层片组成,变形组织含有人量位错及少量变形孪晶.锻态试样抗拉强度(σb),延伸率(δ)分别达到708.1 MPa和0.95%.再通过不同的热处理分别得到晶粒细小的双态组织、近层片组织和全层片组织.经1320 ℃/30 min炉冷后得到双态组织,层片晶粒尺寸(d1)约为20 μm,层片体积分数(ψ1)约为60%,具有最高的δ,约为1-9%,σb约为658.9 MPa,为穿晶和沿晶混合断裂;经1340℃/30 min炉冷后得到近层片组织,dI约为60 gm,ψ1约为95%,O'b约为690.2 MPa,δ约为1.75%,上要为穿晶(层片)断裂;经1370℃/15 min炉冷后得到细小全层片组织(d1约为40 μm),具有最高的σb,约为715.1 MPa,5约为1.51%,为穿晶断裂.     

Microstructure and tensile properties of cast Ti-44Al-4Nb-4Hf-0.1Si-0.1B alloy with refined lamellar microstructures

The tensile properties of a cast Ti-44Al-4Nb-4Hf-0.1Si-0.1B alloy with fine lamellar structures have been measured at room temperature. The average lamellar colony size was in the range of 70–130 μm, depending on heat treatment condition. All the tensile ductilities measured at room temperature are below 0.45% with the majority between 0.3 and 0.4%. Microstructural examination and fractographic examination revealed that there are many lamellar colonies with their lamellar interfaces parallel to each other, in contrast to observations on an extruded sample, which showed 1% ductility. Cleavage along the lamellar interfaces in those parallel colonies in the cast samples forms clusters of small parallel cracks close to each other and their collective effect, together with that from the debonding between boride ribbons and the metal matrix, may contribute to the low ductility in the cast alloy. Analysis shows that those parallel lamellar colonies probably originate from the Burgers alpha grains (obeying Burgers OR with the beta phase) formed during the beta-to-alpha solid phase transformation.     

Effect of Cu addition on corrosion resistance and shape memory effect of Fe- 14Mn-5 Si-9Cr-5Ni alloy

The modification of Fe-14Mn-5Si-9Cr-5Ni shape memory alloys(SMAs) by copper addition was carried out, aiming at further enhancing its corrosion resistance. The results of electrochemical potentiodynamic measurement and immersion test show that copper can remarkably improve the corrosion resistance in Cl- solution. Otherwise, it is found that copper cannot markedly affect the mechanical properties nor the shape memory effect(SME). As for the effects of copper on Fe-Mn-Si based alloys, the austenite strengthening is one of the key factors to improve SME.     

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。     

Ti-25Al-14Nb-2Mo-1Fe合金的热变形行为及本构方程的建立

通过热模拟压缩试验研究了Ti-25Al-14Nb-2Mo-1Fe合金在变形温度950~1100 ℃,变形速率0.001~1 s^-1,最大变形程度50%条件下的热变形行为。结果表明：Ti-25Al-14Nb-2Mo-1Fe合金的流变应力对热变形工艺参数（变形温度和变形速率）的敏感性较高,其真应力-真应变曲线具有峰值应力、应变软化和稳态流动特征。采用Arrhenius双曲正弦函数和多元回归处理法确定了合金在试验条件下的应力指数n、变形激活能Q等材料参数,建立了Ti-25Al-14Nb-2Mo-1Fe合金高温变形本构关系模型。     

Effect of Zr addition on microstructures and mechanical properties of Ni-46Ti-4Al alloy

The microstructures and mechanical properties of Ni-(46-x)Ti-4Al-xZr (x = 0-8, at.%) alloys have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical tests. The results show that the Ni-Ti-Al-Zr alloys are composed of TiNi and (Ti, Al) 2 Ni with Zr as a solid solution element in both phases, and the third phase, (Zr, Ti, Al) 2 Ni, appears in Ni-40Ti-4Al-6Zr and Ni-38Ti-4Al-8Zr alloys. The compressive yield strength at room temperature increases with the increase of Zr content due to the solid-solution strengthening of Zr and precipitation strengthening of (Ti, Al, Zr) 2 Ni phase. However, the Ni-42Ti-4Al-4Zr alloy exhibits the maximum compressive yield strength at 873 and 973 K because of the softening of (Zr, Ti, Al) 2 Ni phase in the alloys with more Zr addition. The tensile stress-strain tests and the SEM fracture surface observations show that the brittle to ductile transition temperature of Ni-42Ti-4Al-4Zr alloy is between 873 and 923 K.     

热暴露对Ti-44Al-4Nb-4Hf-1B合金显微结构和力学性能的影响

对合金Ti-44Al-4Nb-4Hf-1B在700℃大气气氛中开展了长达10 000 h的热暴露处理,系统地探索和分析含Nb-Hf的TiAl合金的高温热稳定性,采用透射电镜和扫描电镜观察合金的显微组织变化并测试相应的力学性能.研究发现:长期大气高温热暴露导致合金中α2+γ层片晶团内的a2层片发生了一定程度的α2→γ相变:部分α2层片转变成为细小的γ层片,到10 000 h时,α2层片的原始厚度减少了约一半.长期大气高温热暴露也导致合金中α2+γ层片条束上发生了α2+γ→B2(ω)相变:条束上部分α2+γ消失,代之以微米及亚微米尺度的B2(ω)块状相.在10 000 h时,其面积分数达到8.4％,随着高温热暴露的逐渐进行,合金的室温塑性伸长率逐渐降低.在10 000h时,合金的塑性约为热暴露前的2/3,表明在复合含Nb+Hf的TiAl合金中,热暴露所导致的“释氧脆化”和“B2+ω生成脆化”的影响有限.复合含Nb+Hf的TiAl合金具有优于单纯含Nb的TiAl合金的高温热稳定性.长期高温热暴露对合金的断裂强度和条件屈服强度没有明显的有害影响.在10 000 h时,其条件屈服强度总体上仍保持在600MPa级别,而合金的室温疲劳极限还有所提高.     

电子束熔丝成形Ti-6Al-3Nb-2Zr-Mo合金的组织与力学性能

试验采用电子束熔丝快速成形方法(EBRM)制备了Ti-6Al-3Nb-2Zr-Mo合金试样,研究了EBRM Ti6321合金化学成分、显微组织、力学性能及冲击韧性. 结果表明,该合金在熔丝成形中Al元素烧损1.0%左右,且合金内部没有元素偏析. EBRM Ti6321合金显微组织为沿沉积高度方向生长、晶贯穿多个沉积层的粗大柱状晶,柱状晶内部以α片层为主. EBRM Ti6321合金x向和z向的室温抗拉强度各项异性系数为2.6%,断裂方式均为韧性断裂. x向和z向冲击韧性均不低于80 J,各向异性系数为3.1%;冲击断口有大量的韧窝,为典型的韧性断裂.     

Ti3SiC2表面渗硅涂层的抗高温氧化性能

采用固体粉末包埋法在Ti3 SiC2 陶瓷上渗硅 ,研究了渗硅涂层的抗高温氧化性能 ,用XRD及SEM /EDS分析了渗硅涂层及其氧化后产物的成分、结构和形貌等。结果表明 :渗硅层主要由TiSi2 和SiC组成 ,在空气中氧化时形成了SiO2 和TiO2 的混合氧化物膜。渗硅样品在 110 0℃和 12 0 0℃下的恒温氧化速率比Ti3 SiC2 降低了 2～3个数量级 ,110 0℃下抗循环氧化性能也优于Ti3 SiC2 。但由于渗硅层中存在裂纹 ,循环过程中当裂纹贯穿整个渗硅层时 ,涂层的氧化速度开始增加 ,其保护作用逐步退化。在 110 0℃下空气中循环氧化时 ,经 40 0次循环后涂层已基本失效。