TG6钛合金冷却过程的块状转变机制研究（英文）

在近α型TG6钛合金两相区淬火过程中,对初生α相α_P周围形成的块状组织α_m进行表征研究,块状组织α_m与α_P存在明显的界面,合金元素Al、Sn和Zr浓度介于α_P和β基体之间,EBSD分析结果表明α_m取向与α_P保持一致。在冷却过程中,α_P周围β基体中合金元素扩散受到限制,进而在局部过渡成分区域通过扩散转变形成α_m组织。当固溶温度从1040℃提高至1060℃,同时保温时间从30 min减少为5 min,溶质元素扩散受限,α_m体积分数从5.2%提升至30.7%     

Zr-2.5Nb合金在550℃/25MPa超临界水中腐蚀时的氢致α/β相变

Zr-2.5Nb合金经a相水淬及冷轧变形后,再经过580℃/5 h和650℃/2 h的热处理,在静态高压釜中进行550℃/25 MPa超临界水腐蚀实验.用电子显微镜研究了腐蚀前、后合金基体的显微组织.结果表明在550℃/25 MPa超临界水中腐蚀到一定程度后,合金基体内会形成氢稳定的β-zr相,同时合金元素Nb扩散进入该相,形成富Nb/H的β-Zr相.该相在降温过程中发生分解,形成ZrHx、α-Zr和Nb含量不同的Zr-Nb相组织.     

固溶时效处理对TC20钛合金α相演变和硬度的影响

采用SEM、TEM、XRD和硬度等技术对先固溶(840 ℃×0.5 h)后不同时效(460 ℃×4 h;320 ℃×15 min→460 ℃×4 h;320 ℃×10 min;460 ℃×10 min)热处理工艺的TC20合金试样进行了观察与表征,研究TC20合金的α相对时效过程中β→α相转变。结果表明:热轧态组织由α相与β相共同组成,固溶态组织相中生成了许多小尺寸α相。采用460 ℃×4 h进行处理试样内形成了片状分布的α相,采用320 ℃×15 min→460 ℃× 4 h处理试样内形成了具有更小长宽比的α相,并且该试样内的大部分α相尺寸均接近100 nm。两种时效方法形成的第二相都是α相,采用320 ℃×15 min→460 ℃×4 h处理具有尺寸更加细小的α相。当温度到达460 ℃时更多α相可以通过ω相进行形核,从而在β基体上形成致密均匀分布状态。采用320 ℃×15 min→460 ℃×4 h处理后合金中的ω相已不存在,同时析出了更多的α相,合金硬度高达503 HV,显著高于β基体的硬度,α相可以促进合金硬度的大幅提升。     

不同合金元素对Mg15Al镁合金显微组织与腐蚀性能的影响

研究了Zn、Si、Nd三种元素对Mg15Al镁合金微观组织和腐蚀性能的影响,通过金相显微镜和XRD分析了Mg15Al-X合金的显微组织。结果表明:三种元素都能使Mg15Al合金的晶粒细化,Nd的细化效果最好。Mg15Al-1Zn中不出现新相,但是Zn的加入可促进β相的形成,而Mg15Al-1Si和Mg15Al-1.5Nd中分别出现了汉字状或块状新相Mg2Si和针状新相Al11Nd3,促使β相成均匀连续网状结构。添加Si元素,增加了β相含量,Mg2Si相与β相形成屏障保护α-Mg基体;添加Nd元素,β相含量减少,抑制了α-Mg基体与β相之间的微电偶腐蚀,从而提高了Mg15Al合金的耐腐蚀性。     

Ti-43.5Al-4Nb-1Mo-0.3B合金中β相行为和特征

采用元素粉末经热压烧结法制备了新型Ti-43.5Al-4Nb-1Mo-0.3B合金,研究了热处理工艺对合金组织中β相转变行为及其力学性能的影响。结果表明,粉末冶金态Ti Al合金中β相呈条带状,与γ相形成块状组织。热处理能显著改善材料的组织均匀性,使B2/γ块状组织逐渐转变成α_2/γ层片组织,β相转变行为特征为吸收Ti、Al元素,排出Nb元素。温度是热处理过程中组织均匀化的主控因素,在共析温度Te附近热处理时(1100~1160℃/24 h),B2相逐渐溶解但不能完全消除,而在α相转变温度Tα以上短时热处理和稳定化低温热处理后,如1400℃/2 h/FC+850℃/6 h/AC,B2/γ块状组织可完全消除,且组织粗化不严重。初始态B2相纳米硬度为6.69 GPa,弹性模量为175.4 GPa,热处理导致其纳米硬度和弹性模量逐渐降低。     

钛表面辉光等离子渗钯过程中Pd在钛中扩散行为的研究

采用辉光等离子冶金技术在纯钛表面制备了Ti-Pd合金层,用XRD、SEM和EDS研究合金层的相组成、微观组织和元素分布。结果表明:900℃渗钯时,Ti-Pd合金层大体分为3层,各层间Pd元素的浓度有明显的突变,Pd在Ti中的扩散属于反应扩散。室温状态时,合金层从表层到基体分别是:Ti Pd3相层,α-Ti Pd相层,Ti2Pd相层。推测合金层在高温状态时,从表层到基体分别是:Ti Pd3相层,β-Ti Pd相层,Pd在β-Ti中的饱和固溶体层。各层的长大速率基本满足抛物线规律,Pd在Ti中的扩散以体扩散为主。     

SiC_f/Ti-43Al-9V复合材料的基体微观组织

采用箔-纤维-箔法和1150℃/150 MPa/30 min的真空热压工艺成功制备了SiCf/Ti-43Al-9V复合材料,并使用金相显微镜、X射线衍射仪、扫描电镜及能谱仪对该复合材料微观组织的形成进行了研究。结果表明,制备过程中SiC纤维与TiAl基体合金发生反应,并形成一定厚度的反应层;基体组织为等轴晶,粒径约为8μm,与原始合金组织相比明显细化;从反应层到远处的TiAl基体合金,基体合金的组织由全γ相转变为α2/γ片层组织、γ晶粒和晶间B2相的混合组织。其中全γ相区域的厚度为2～4μm,并围绕纤维分布。根据Ti-Al-V相图、C原子和V原子的扩散,分析了这两个基体区域的形成机理,并结合热压成形过程中的塑性变形和变形储存能,解释了基体合金晶粒大小的变化。     

磁性Fe3O4/Ag复合纳米粒子制备与抗菌性能

采用箔-纤维-箔法和1150℃/150 MPa/30 min的真空热压工艺成功制备了SiCf/Ti-43Al-9V复合材料,并使用金相显微镜、X射线衍射仪、扫描电镜及能谱仪对该复合材料微观组织的形成进行了研究.结果表明,制备过程中SiC纤维与TiAl基体合金发生反应,并形成一定厚度的反应层;基体组织为等轴晶,粒径约为8 μm,与原始合金组织相比明显细化;从反应层到远处的TiAl基体合金,基体合金的组织由全γ相转变为α2/γ片层组织、γ晶粒和晶间B2相的混合组织.其中全γ相区域的厚度为2～4 μm,并围绕纤维分布.根据Ti-Al-V相图、C原子和V原子的扩散,分析了这两个基体区域的形成机理,并结合热压成形过程中的塑性变形和变形储存能,解释了基体合金晶粒大小的变化.     

低冷速对Mg-Al合金晶粒尺寸及β相的影响

在Ar保护条件下获得冷却速度为1、2、3、4和5℃/min的Mg-6Al和Mg-10Al合金,利用光学显微镜、扫描电镜、能谱分析和Imagetool软件研究慢冷对Mg-6Al和Mg-10Al合金晶粒尺寸以及β相分布特征与数量的影响。结果表明,Mg-6Al和Mg-10Al合金凝固组织由α-Mg相、点状和层片状析出β-Mg17Al12相以及棒状(α+β)共晶组成。随着冷速从5℃/min减小到1℃/min,Mg-6Al与Mg-10Al合金组织中α-Mg晶粒尺寸分别由195.7、180.4μm增至318.7、225.1μm,与此同时β-Mg17Al12相的数量分别由24.56%、45.50%降至18.36%、38.59%。     

Effect of α Composite Layer on the Microstructure and Mechanical Properties of Ti-10V-2Fe-3Al Alloy

通过在830℃空气中保温1 h后水冷的热处理工艺,在Ti-10V-2Fe-3Al(Ti1023)钛合金表面形成厚度约为82μm的α富氧复合层。研究了α复合层内显微组织形貌、硬度及元素分布特点及复合α层后对Ti1023合金组织和性能影响。结果表明:α复合层从边缘到基体内部硬度值并非一直减小,而是呈现高-低-高-低-趋于稳定的变化规律。研究表明硬度变化规律与合金元素(尤其V、Fe)及组织形态分布相关。Ti1023合金试样复合α层后表面硬度增加了45%,而屈服强度和抗拉强度下降5%。在拉伸变形过程中,复合α层后试样首先会在垂直于拉伸应力方向的外表面产生裂纹,之后裂纹扩展穿过α层到基体内部直至试样断裂,试样拉伸断口呈现心部韧性断裂和边部脆性断裂特征。拉伸过程中试样内部存在应力诱发β相向α″相的组织转变。     

Typical Microstructural Characteristics of Ti-5Al-5Mo-5V-3Cr-1Fe Metastable βTi Alloy Forged in α+β Region

In this study, typical microstructural characteristics of a metastable β Ti alloy (Ti-5Al-5Mo-5V-3Cr-1Fe) forged in a dual-phase region (strain of 54% at 820 °C) were investigated in detail by the combined use of X-ray diffraction, energy dispersive spectroscopy, electron channeling contrast imaging and electron backscatter diffraction techniques. Results show that the microstructure of the forged alloy is composed of bulk α grains, α plates and β matrix. The bulk α grains correspond to retained primary α phase (α_p, average grain size~2.4 μm), while the α plates are secondary α phase (α_s, width~70 nm) precipitated from the β matrix during air cooling. During forging, the β matrix experiences dynamic recovery with many subgrains and significant orientation gradients formed. Analyses of the orientation relationship between the α and β phases show that the Burgers orientation relationship is not maintained between some α_p and β phases, which should be related to thermal deformation-induced changes of their orientations. In contrast, all of the α_s plates are found to maintain well the Burgers orientation relationship with the β phase.     

Microstructure and mechanical properties of Ti-6Al-4V/Ti-22Al-25Nb joint formed by diffusion bonding

Ti-6Al-4V (wt.%) and Ti-22Al-25Nb (at.%) were joined by diffusion bonding at 950 °C and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of the diffusion layer is B2/discontinuous α/α₂ layer/necklace-shaped β+α′ layer, where the content of any element at a given point mainly depends on the distance of the point from the interface and the phase type at the point. The tensile strength of the joint is 894 MPa, which is almost the same as that of the Ti-22Al-25Nb base alloy. The fracture surfaces on both sides of the joint are composed of two main regions. One region displays a relatively flat surface and fractures along the bonding interface. The other is composed of a moderate number of irregularly-shaped cavities on the Ti-6Al-4V side and many irregularly-shaped bulges on the Ti-22Al-25Nb side. Both regions result from fracture along the boundaries between β+α′ layers and α_p grains or from the transcrystalline fracture of α_p grains.     

Pb-Bi-Sn准包晶合金定向凝固微观组织演化

采用液态金属冷却定向凝固结合液淬法,在温度梯度为18 K/mm、凝固速度为0.5～100 μm/s的条件下系统研究了Pb-30％Bi- 18％Sn准包晶合金的微观组织演化及溶质分布规律.主要从凝固路径、相组成、溶质分布及微观组织特征等几个方面来研究Pb-Bi-Sn准包晶合金定向凝固过程的组织演化.其中,准包晶合金的凝固路径通过DSC差热分析的方法进行研究,发现其凝固路径为:L→L+α-Pb→L+α-Pb+β-Pb7Bi3→L+α-Pb+β-Pb7Bi3+Sn→ (β-Pb7Bi3+Sn)共晶.结合XRD,分析定向凝固试样的相结构,结果表明:试样由具有面心立方结构的α-Pb相、密排六方结构的β-Pb7Bi3相和体心正方结构的(Sn)相构成.在Pb-Bi-Sn合金定向凝固过程中,当凝固速度为0.5～2 μm/s时,初生α-Pb相以胞状界面生长,而当凝固速度增大至5μm/s及以上时,初生α-Pb相将由胞状转变为枝晶状界面生长.利用能谱分析仪对定向凝固试样进行溶质分布测试,发现局部出现溶质偏析,导致共晶组织(β-Pb7Bi3+Sn)出现.     

焊丝成分对铝/铜激光熔钎焊接头组织和性能的影响

通过添加Zn-Al焊丝成功实现了2A16铝合金/T2铜异种材料的激光熔钎焊连接,并采用扫描电子显微镜和能谱仪对接头的微观组织进行表征,同时,研究了Zn-2％Al,Zn-5％Al和Zn-10％Al?3种焊丝对接头成形、微观组织以及力学性能的影响.结果表明,铝/铜激光熔钎焊接头主要由CuZn相,Al2Cu相,Al4Cu9相...     

Dislocation Slip and Crack Nucleation Mechanism in Dual-Phase Microstructure of Titanium Alloys: A Review

The study on the deformation mechanism of titanium alloys is beneficial to revealing the influence of microstructure on mechanical properties, and then providing guidance for the optimization of microstructure and properties. For most near-α and α + β titanium alloys, slip is the dominant deformation mechanism. Therefore, investigating the slip initiation and slip transfer behavior, as well as crack nucleation mechanism, is essential to reveal the fundamental relationship between microstructure and mechanical properties. However, due to the coexistence of grain boundary and phase boundary in dual-phase microstructure of titanium alloys, the phase content, grain size, grain boundary misorientation and α/β orientation relationship would affect the slip initiation and transfer behavior, resulting in a very complex plastic deformation mechanism. Based on the previous investigations of deformation mechanism of near-α and α + β titanium alloys, this review first analyzed the sequence of slip initiation between α and β phases and discussed the main factors affecting the slip initiation in α phase. Secondly, the basic rule of slip transfer and the influence of different interfaces on slip transfer were reviewed. Finally, the mechanism of crack nucleation and effect of microstructure on crack nucleation were analyzed based on slip transfer behavior.     

汽车发动机用AZ91D合金的表面喷涂与性能

采用热喷涂工艺在压铸态AZ91D合金表面制备了Al涂层,研究了热处理温度和保温时间对AZ91/Al涂层界面组织形貌的影响,并对比分析了扩散层的耐腐蚀性能和耐磨性能。结果表明,热处理前Al涂层与基材为机械结合,热处理后Al涂层与AZ91合金基材的界面处可形成冶金结合扩散层,且随着保温时间延长,扩散层厚度不断增加;热处理温度在375 ℃以下时扩散层主要由β-Mg₁₇Al₁₂相构成,375 ℃×8 h热处理后为α-Mg+β-Mg₁₇Al₁₂相,425 ℃×1 h热处理后为γ-Mg₂Al₃和β-Mg₁₇Al₁₂相。AZ91合金基材和扩散层腐蚀电位从高至低顺序为γ>β>α+β>AZ91合金基材,扩散层的腐蚀电流密度均低于AZ91合金基材,阻抗谱图中容抗弧半径从大至小顺序为γ>β>α+β>AZ91合金基材,扩散层的耐腐蚀性能均优于AZ91合金基材;γ、β和α+β扩散层的摩擦稳定性系数都高于AZ91合金基材,而磨损速率和磨痕宽度都要小于AZ91合金基材,其中β扩散层的磨损速率和磨痕宽度最小,具有最佳的抵抗磨损的能力。     

Room temperature deformation and mechanisms of slip transmission in oriented single-colony crystals of an α/β titanium alloy

Primary creep at low homologous temperatures and low stresses has been widely reported in α/β Ti alloys. Creep in these alloys is dependent on microstructure, with the colony microstructure showing the least creep resistance. There exists a Burgers orientation relationship between the α and the β phase, which has been assumed to allow for easy slip transmission across the α/β interfaces. Constant strain rate and creep tests were performed on single-colony crystals of a near-α alloy oriented for slip along different prismatic slip systems in the α phase. A distinct anisotropy in the deformation behavior of different colony crystals is found. The origin of this anisotropy is due to the relative misalignment of the slip systems between the α and the β phases which results in the formation of residual dislocations during slip transmission. A simple model is presented based on the accumulation of residual dislocations at both the α/β interface and the α matrix, which provides insight into the mechanism of slip transmission, strain hardening and primary creep of these colony structures.     

β-ZrTiAlV合金炉冷过程中的组织演变

结合EBSD和XRD,系统地研究了β-51.1Zr40.2Ti4.5Al4.2V合金在炉冷过程中3种α相(αGB、αWGB和αWI)的形核机制以及α含量对合金性能的影响。结果表明:炉冷过程中,在原β界面处具有{0001}面平行于相邻β晶粒共有{110}面取向特征的α相(αGB)会优先形核;αWGB主要以界面不稳定形核为主,通过继承αGB的取向并向原β晶内生长,从而在晶界附近形成平行板条区;为了协调相变过程中产生的形状应变,αWI通过自协作机制产生三变体团簇,且形成三变体团簇的变体之间相互满足60°/1120取向关系;随着炉冷后保温温度的降低,α相的相对含量增加,合金的硬度增大,且硬度和α相的相对含量存在一定的线性关系。     

Ti-55531合金变形及断裂行为的原位SEM分析

采用原位SEM拉伸方法对比分析了Ti-55531合金片层和双态组织静载下的变形及断裂行为。结果表明,静载下α相的特征参数对该合金的形变、裂纹萌生及扩展有强烈影响。片层组织中粗大次生αs片较软,αs片最先变形促进位错滑移,位错运动至次生αs和残留βr的界面处堆积,塑性变形导致局部应力集中促进裂纹萌生,并沿αs/βr相界面扩展。双态组织中初生等轴αp是相对最软相且尺寸较大,位错滑移自由程较大,易启动多系滑移,αp内不同位向的滑移线交割促进应力集中,部分位错在αP/βtrans界面处堆积产生应力集中,两者导致微裂纹萌生于αp内及αp/βtrans界面,并沿αp/βtrans界面和αp聚集处扩展。     

深潜器用Ti80电子束焊接接头精细组织结构特征

进行了Ti80大厚板电子束焊接试验,实现了56 mmTi80无缺陷焊接.分析焊缝和热影响区精细组织,结果表明,焊缝上部为柱状晶粒,下部为柱状晶和等轴晶,晶粒内组织为马氏体α相和残余β相.焊缝由上至下高温停留时间逐渐减小、冷却速度逐渐加快,马氏体α相呈长大趋势.热影响区分为靠近焊缝区的Ⅰ区和靠近母材的Ⅱ区.热影响Ⅰ区组织为马氏体α相、初生α相和β相;Ⅱ区组织为初生α相、次生α相和转变β组织.Ⅰ区由于受热影响作用大,其组织更接近于焊缝;Ⅱ区组织则更接近于母材组织.