文献翻译-钛合金相变超塑性连接技术研究

外文资料翻译
Transformation Super plasticity of Titanium Alloy
Technology Research Connection
The outstanding characteristic of titanium is its high specific strength and excellent corrosion resistance, while at the same time has good heat resistance and low temperature performance, and practical application of a wide range. As long as the materials properly, not only can greatly increase the effectiveness of equipment, but also can bring significant economic benefits. In regard to corrosion resistance, titanium alloys in oxidizing and neutral media is extremely stable, the corrosion rate in sea water is far below the stainless steel, compared with platinum, it is suitable for the petroleum, chemical, electric power, metallurgy, agricultural chemicals, paper-making, shipbuilding, food and medical applications and health departments.
Due to the characteristics of titanium alloy with the above, it is particularly suitable for aircraft and spacecraft materials design is required. Aviation Industry Development and Application of titanium alloys is the first sector. The beginning of the fifties, the United States succeeded in the use of a titanium aircraft, although at the time of each aircraft being used for only 1% the weight of the structure of titanium, but titanium has opened up applications in the aviation industry in the broad road. Now, the titanium in the world has been widely used, small screws, nuts, such as connectors, up to the fuselage frame, every other frame, such as structural parts, and even more than 6 meters long, weighing two tons of the main support beam of the landing gear. For high-speed fighters, as a result of high-speed and high maneuverability, the aircraft structure as far as possible the requirements of light, heat capacity at the same time; practice has proved that titanium is the most appropriate material.
Titanium is the world's recognized difficult-to-machine materials, but the
use of super plastic forming / diffusion bonding process (SPF / DB) can be produced by welding, riveting processes difficult to produce complex titanium aircraft parts and components to enable integration, light weight, and lower the cost.
Use of materials under thermal cycle repeated phase-change role in the effects of pressure welding material so that the contact took place in super plastic flow, so that the surface in close contact and close to the inter-atomic forces to achieve the scope of , the realization of the material on both sides of the interface connected to a reliable welding method known as phase-change Super plastic diffusion bonding (Transformation Super plastic Diffusion Bonding). Super plastic conditions, the material under stress in the smaller plastic deformation has a very good ability to flow the process of super plastic materials in a highly activated state of atoms, these materials will help to remove the surface oxide film to improve the combination of the close connections and speed up the atomic diffusion, resulting in a short period of time to achieve a reliable connection. Be welded as long as the phase-change material, the use of such methods can be welded. Repeated phase-change material is produced by thermal cycling to achieve, and therefore thermal cycling method has become the core of this welding process links.
Phase transformation super plastic diffusion bonding is a solid-phase welding method, a general proliferation of welding and the characteristics of welding deformation, deformation mechanisms and the proliferation of mechanisms in the formation of welded joints are equally important role in the process. Phase transformation super plastic diffusion bonding joints or less after the formation of three phases.
First, physical contact with the formation of phases:
To the formation of the actual physical contact, the material must be removed on the surface oxide film and the adsorbed layer, but in the welding process and welding can completely clear the oxide film is of utmost importance. Vacuum welding, the adsorbed layer and the oxide film under high
temperature description, distillation, evaporation, chemical reaction and dissolution methods can be eliminated.
In the process of diffusion bonding, only the material near the surface of each other, reaching between atoms can be caused by physical distance, will it be possible to form a welded joint quality. In general, the solder materials were processed through sophisticated, from the micro-view of its surface is still uneven. Therefore, in the beginning stages of diffusion welding, the welding material contact surfaces can only form of local contacts, while the remainder of the full contact is required by the interface of the plastic deformation of solder material, there is no part of the full contact holes are formed, the holes on the formation of adverse effect on joint reliability.
Phase change materials in the super plastic deformation resistance under conditions of low stress in the low to the high occurrence of plastic deformation, welding interface of the holes can exist in the role of high-plastic archeology to be filled rapidly. Phase-change material, the grains continue to migration and conversion, the surface oxide film to break down quickly broken. The use of phase-change method of super plastic diffusion bonding can be smaller under the pressure of the rapid realization of fully welded joint physical contact.
Second, chemical interaction of stages:
The formation of the actual contact and the surface is not enough to have a strong connection between atoms. In order to obtain the combination of atoms between the solid, it is necessary to activate the surface atoms. Activation of the surface atoms will lead to the original bond (for example, the chemical adsorption and oxygen level) of the tear, and then will it be possible to make the electronic interactions between atoms. Under the metal in the external force generated by shear stress and normal stress can cause the metal surface of the plastic deformation and flow, plastic deformation and flow of cause defects in the crystal structure (dislocations and hole) to move to the surface at this time, defect migration the release of atomic energy will activate
the surface, the formation of activation centers. If the higher temperature, the surface will activate the number of centers is increasing rapidly. Surface and then welded between the two has to activate the interaction between the atoms combine.
Transformation Super plasticity make plastic welding surface archeology, the archeology of plastic to broken oxide film and increase the dislocation density and the hole with the speed of migration. After breaking the oxide film to form a "fresh, the surface, this surface has a higher degree of chemical activity. At the same time, phase change as a result of recrystallization and dynamic recrystallization of the repeated changes in the grain boundary and repeated migration, so that atoms have a high interface activity.
Third, the interaction of body phases:
Is through a combination of metal materials for the spread around the stage. In welding with the metal, the sign of the end of the third phase is generated in the joint of the recrystallization process, a common grain. Dissimilar metal welding, whether or not to limit the spread of the third phase of the process depends on the nature of the proliferation zone and the resulting nature of the new phase. Transformation Super plasticity of the tremendous role in promoting proliferation, could have been welding in a short time. Application of super plastic titanium alloy connectivity features: First, can the past by a number of parts by mechanical connection or welding together the major components assembled in a heated, pressurized process of forming the overall structure for large pieces, greatly reducing the number of parts and tooling to shorten the manufacturing cycle, reduced the manufacturing cost.
Second, designers can provide greater flexibility to design a more rational structure to further improve the efficiency of the structural load to reduce the structural weight.
Third, the use of this technology to create comprehensive maps of the structure, and material after the diffusion bonding interface completely
disappeared, so that the entire structure as a whole, has greatly improved the structure of the anti-fatigue and anti-corrosion properties; and through appropriate structural design can also improve the structure of the bending rigidity, and expand the scope of application of titanium alloys. Industrial base, such as air days of the titanium alloy used in cold forming and machining is very difficult to make it practical subject to certain restrictions, SPF / DB titanium technology enables a simple manufacturing process, can be achieved almost at the same time more than technology The precise amount of processing, improved material utilization, reduced production costs.
Fourth, the material in the process of super plastic forming can withstand great deformation without rupture, you can shape the structure of a very complex matter, which is the conventional method of cold forming the basic shape can not do or need to be achieved on many occasions. Super plastic forming material in the course of flow stress is very small, this can be used in small tonnage of equipment forming the structure of large pieces of the structure and processing of non-resilient, non-residual stress, high-precision forming.
U.S. aircraft manufacturer in the early seventies began to study the super plastic forming technology of titanium alloy (SPF), in 899 ~ 927 ℃high temperature and strain rate of 10-4 cm / s under the conditions so that an extension of titanium alloys rate of 60 to 1000%, the sample forming process a vacuum forming plastic board as the same does not occur in the case of necking and fracture under the uniform deformation of the complex.
At present, the United States has in the four models using Ti-6AL-4V super plastic forming (SPF) components, the number reached 256. One of "AV-18" 74 pieces, "F-25" 77 pieces, "F-18" 29 pieces, "B1-B" 76 pieces. Using super plastic forming process for the "F-18" has produced 5000 parts, and the number is increasing, the company's three meters in diameter "F-20" body frame, is also planning the use of two semi (SPF) forming process. Titanium alloy in the super plastic forming process conditions, diffusion
bonding can be carried out.
In the mid-seventies, the U.S. Air Force commissioned a company in Rockville (SPF / DB) process "B1-B" beams framework engine aircraft, the 12 parts of Ti-6AL-4V sheet metal forming, reducing the weight than the original 39%, reduced costs by 43%, dispense with the fastener 81.
At present, for the purpose of establishing the U.S. Air Force (SPF / BD) technology is pursuing a (BLATS) plan that is ready to create a low-cost structure of advanced titanium alloys plan. As part of the plan, Rockville Company has successfully created a lot of titanium aircraft parts. The largest component in the body has reached 454 kilograms, length of 102 centimeters, width of 429 centimeters, and the thickness of 25-71cm. After the body parts to achieve size 41x163x168cm, and the use of original parts manufacturing process compared to 32% weight, the cost dropped by 41%.In 1981, the U.S. Air Force component of the load under the assumption that the two tests to verify its reliability, testing 4000 hours to do the first time the successful conduct of the 8000 hours. In the second test, the parts intended to crack the main site of occurrence, the pilot process to intentionally damage, is still facing a test of 8000 hours. It can be seen, (SPF / DB) titanium alloy forming technology of high reliability components
钛合金相变超塑性连接技术研究
钛合金的突出特点在于它的高比强度及优良的耐腐蚀性，同时又具有良好的耐热性和低温性能，因而实用性强，应用面广。

只要选材得当，不仅能大大提高装备的工作效能，同时也可以带来明显的经济效益。

在耐腐蚀性方面，钛合金在氧化性及中性介质中极为稳定，在海水中的腐蚀速率远远低于不锈钢，可与白金媲美，故适于在石油、化工、电力、冶金、农药、造纸、造船、食品及医疗卫生等部门应用。

由于钛合金具有以上特点，所以它特别适合于飞机和航天器的材料设计需要。

航空工业是研制和应用钛合金最早的部门。

五十年代初，美国成功地在飞机上使用了钛，虽然当时每架飞机只用了百分之一结构重量的钛，但开拓了钛在航空工业中应用的广阔道路。

现在，钛合金已经在世界上得到广泛应用，小至螺钉、螺母等连接件，大至机身骨架、隔框等结构件，甚至六米多长、重达两吨的起落架主支撑梁。

对于高速战斗机，由于高速和高机动性，要求飞机结构尽可能轻，同时还要耐高温能力，实践证明，钛合金是最适宜的材料。

钛合金是世界上公认的难加工材料，但是利用超塑性成形/扩散连接工艺(SPF/DB)可以制作出用焊接、铆接工艺方法难于制作的复杂的钛合金飞机部件，并且使部件一体化、轻量化，成本降低。

利用材料在热循环的作用下的反复相变作用，在压力的作用下使被焊材料在接触面处发生超塑性流变，从而使表面紧密接触并接近到原子间作用力能达到的范围之内，实现界面两侧的材料的可靠连接的焊接方法称为相变超塑性扩散焊接（Transformation Super plastic Diffusion Bonding）。

超塑性条件下，材料在较小应力下具有非常好的塑性变形能力，超塑性流变过程中材料原子处于高度活化状态，这些有利于去除材料表面氧化膜、提高接头结合的紧密性和加快原子扩散，从而在短时间内实现可靠连接。

只要被焊接材料具有相变点，就可能用这种方法进行焊接。

材料的反复相变，是通过热循环来实现的，因此热循环就成了这种焊接方法的核心工艺环节。

相变超塑性扩散焊接是一种固相焊接方法，具有一般扩散焊接和变形
焊接的特点，变形机制和扩散机制在其形成焊接接头的过程中的作用同等重要。

相变超塑性扩散焊接形成接头大致经过三个阶段。

一、物理接触的形成阶段：
要形成实际的物理接触，必须清除材料表面上的氧化膜和吸附层，但是在焊前和焊接过程中能否彻底清除氧化膜是至关重要的。

真空焊接时，吸附层和氧化膜在高温下通过解吸、升华、蒸发、化学反应和溶解等方法可以消除。

在扩散焊接过程中，只有材料表面相互靠近，达到原子间能够引起物理作用的距离，才有可能形成优良的焊接接头。

一般地，被焊材料经过精密加工后，其表面从微观来看仍然是凹凸不平的。

因此，在扩散焊开始阶段，被焊接材料接触面只能形成局部的接触，而剩余部分的充分接触则需要界面处被焊接材料的塑性变形，没有充分接触的部分则会形成孔洞，这些孔洞对形成可靠接头有不利影响。

材料在相变超塑性条件下的变形抗力很低，在低应力下即可发生高塑性变形，焊接界面处存在的孔洞可以在高塑性流变的作用下迅速得到填补。

材料相变时，晶粒不断地迁移和换位，促使表面氧化膜快速破碎分解。

利用相变超塑性扩散焊接方法可以在较小的压力下快速实现焊接接头的充分物理接触。

二、化学的相互作用阶段：
形成实际接触时，所产生的还不足以产生表面原子间的牢固连接。

为了获得原子之间牢固的结合，就必须激活表面的原子。

表面原子的激活将会导致原有的原子键(例如与氧的化学吸附层)的撕裂，此后才有可能使原子间的电子相互作用。

金属在外力作用下所产生的切应力与正应力会引起金属表面的塑性变形和流动，塑性变形和流动会使结晶组织中的缺陷(位错和空穴)迁移到表面，此时，缺陷迁移释放的能量会使表面原子激活，形成激活中心。

如果升高温度，表面激活中心的数量会迅速增加。

然后两个被焊表面之间已经激活的原子产生相互作用而结合。

相变超塑性使焊接表面产生塑性流变，这种塑性流变能破碎氧化膜和增加位错与空穴的密度与迁移速度。

氧化膜破碎后，形成“新鲜，，表面，这种表面具有很高的化学活性。

同时由于相变重结晶和动态再结晶的反复
进行，晶界反复发生变化和迁移，使界面原子具有很高的活性。

三、体的相互作用阶段：
就是金属材料通过结合面向周围进行扩散的阶段。

在焊接同种金属时，第三阶段结束的标志是在接头处产生再结晶过程，形成共同晶粒。

异种金属焊接时，是否要限制第三阶段的扩散过程，取决于扩散区的性质和产生的新相的性质。

相变超塑性对扩散的巨大促进作用，可以使焊接过在较短时间内完成。

钛合金超塑性连接技术应用特点：
一、可使以往由许多零件经机械连接或焊接组装在一起的大部件在一次加热、加压过程中成形为大型整体结构件，极大地减少了零件和工装数量，缩短了制造周期，降低了制造成本。

二、可为设计人员提供更大的自由度，设计出更合理的结构件，进一步提高结构承载效率，减轻结构件重量。

三、采用这种技术制造的结构图件整体性好，材料在扩散连接后的界面完全消失，使整个结构成为一个整体，极大地提高了结构的抗疲劳和抗腐蚀等特性；并通过恰当的结构设计还可以提高结构图的抗弯刚度，扩大钛合金的应用范围。

如航空工业基础中常用的钛合金冷成形和机械加工都很困难，使其实用性受到一定的限制，SPF/DB技术则可使钛合金制造工艺简单易行，同时可以实现几乎有工艺余量的精确加工，提高了材料的利用率，降低了生产成本。

四、材料在超塑成形过程中可承受很大的变形而不破裂，可以成形出很复杂的结构件，这是用常规的冷成形方法根本做不到或需多次成形方能实现的。

材料在超塑成形过程中流动应力很小，这样可以用小吨位的设备成形大的结构件，且加工的结构件无回弹，无残余应力，成形精度高。

美国的飞机制造商于七十年代初期开始研究钛合金的超塑性成形工艺(SPF)，他们在899～927℃的高温和变形速率为10厘米/秒的条件下，使钛合金的延伸率达到60～1000%，试件成形过程就像塑料板真空成形一样，在不发生缩颈和断裂的情况下进行均匀的复杂变形。

目前，美国已在四个机种上采用Ti-6AL-4V超塑性成形(SPF)零件，数量达到256个。

其中“AV-18”74件，“F-25”77件，“F-18”29件，“B1-B”
76件。

诺斯罗卜公司利用超塑性成形工艺为“F-18”先后生产了5000个部件，而且数量还在增加，该公司直径为3米的“F-20”机体框架，也计划分两半采用(SPF)工艺成形。

钛合金在超塑性成形工艺条件下，也可以进行扩散连接。

在七十年代中期，美国空军委托罗克维尔公司采用(SPF/DB)工艺制造“B1-B”飞机的发动机横梁框架，该部件采用12块Ti-6AL-4V薄板成形，重量比原来减轻了39%，成本下降了43%，省掉了81个紧固件。

当前，美国空军为确立(SPF/BD)工艺，正在推行一项(BLATS)计划，即准备制造出低成本先进钛合金结构件计划。

作为该计划的一部分，罗克维尔公司已成功地制造出大量的钛合金飞机部件。

最大中机身部件已达454公斤，长度达102厘米，宽度429厘米，厚度25至71厘米。

后机身部件尺寸达到41x163x168厘米，与采用原来制造工艺的部件相比，重量减轻了32%，成本下降了41%。

1981年，美国空军将该部件在假定负荷下进行了两次试验，以验证其可靠性，试验规定做4000小时，第一次成功地进行了8000小时。

在进行第二次试验时，故意使部件主要部位发生裂纹，试验过程中故意让其损坏，仍然承受了8000小时的试验。

由此可见，(SPF/DB)工艺成形的钛合金部件具有很高的可靠性。