The metal titanium (Ti) and its alloys have many attributes which are attractive as structural materials, but they also have one major disadvantage, high initial cost. Nevertheless, Ti and Ti alloys are used extensively in airframes, gas turbine engines (GTE), and rocket engines (RE). The high cost is a deterrent, particularly in airframe applications, in that the other alloys it competes with are, for the most part, significantly lower cost. This is less of a concern for GTE and RE where the cost of titanium is closer to and sometimes even lower than some of the materials it competes with for these applications. In spacecraft the weight savings are so important that cost is a lesser concern. Ti and its alloys consist of five families of alloys; α-Ti, near α-alloys, α + β alloys, β-alloys, and Ti-based intermetallic compounds. The intermetallic compounds of primary interest today are those based on the compound TiAl which, at this time, are only used for engine applications because of their higher temperature capability. These TiAl-based compounds are used in a relatively low, but growing, amounts. The first production application was for low pressure turbine blades in the GE engine (GEnx) used on the Boeing 787, followed by the GE LEAP engine used on A-320neo and B-737MAX. These air foils are investment cast and machined. The next application is for the GE90X which will power the Boeing B-777X. These air foils will be made by additive manufacturing (AM). Unalloyed titanium and titanium alloys are typically melted by vacuum arc melting and re-melted either once (2X VAR) or twice (3X VAR); however a new and very different melting method (cold hearth melting) has recently become favored, mainly for high performance applications such as rotors in aircraft engines. This process resulted in higher quality ingots with a significant reduction in melt-related defects. Once melted and cast into ingots, the alloys can be processed using all the standard thermomechanical working and casting processes used for making components of other types of structural alloys. Because of their limited ductility, the TiAl-based intermetallic compounds are quite difficult to process using ordinary wrought methods. Consequently, the low-pressure turbine blades currently in service are investment cast and machined to net shape. The AM air foils will require minimal machining, which is an advantage. This paper describes some relatively recent developments as well as some issues and opportunities associated with the production and use of Ti and its alloys in aerospace components. Included are new Ti alloys, new applications of Ti alloys, and the current status of several manufacturing processes including a discussion of the promise and current reality of additive manufacturing as a potentially revolutionary method of producing Ti alloy components.

中文翻译：

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钛合金在航空航天零部件中的应用机遇与问题

金属钛（Ti）及其合金具有许多作为结构材料具有吸引力的属性，但它们还有一个主要缺点，即较高的初始成本。尽管如此，Ti和Ti合金仍广泛用于机身，燃气涡轮发动机（GTE）和火箭发动机（RE）。高成本是一种威慑力，特别是在飞机机身应用中，因为与之竞争的其他合金在很大程度上降低了成本。对于GTE和RE，钛的成本接近甚至有时甚至低于与之竞争的某些材料的GTE和RE所关心的问题。在航天器中，减轻重量是如此重要，以至于成本就不再那么重要了。Ti及其合金由五族合金组成。α-Ti，近α合金，α+β合金，β合金和Ti基金属间化合物。当今主要关注的金属间化合物是基于化合物TiAl的那些，由于其较高的温度能力，目前仅用于发动机应用。这些基于TiAl的化合物的用量相对较低，但仍在增长。第一个生产应用是用于波音787发动机的GE发动机（GEnx）的低压涡轮叶片，随后是A-320neo和B-737MAX发动机的GE LEAP发动机。这些空气箔经过精密铸造和机械加工。下一个应用是GE90X，它将为波音B-777X提供动力。这些空气箔将通过增材制造（AM）制成。非合金钛和钛合金通常通过真空电弧熔化进行熔化，然后再熔化一次（2X VAR）或两次（3X VAR）。然而，近来一种新的，非常不同的熔化方法（冷炉床熔化）已受到青睐，主要用于高性能应用，例如飞机发动机的转子。此过程可产生更高质量的铸锭，并显着减少与熔体相关的缺陷。一旦熔化并铸造成锭，就可以使用用于制造其他类型结构合金部件的所有标准热机械加工和铸造工艺来加工合金。由于其有限的延展性，基于TiAl的金属间化合物很难用普通的锻造方法进行加工。因此，对目前使用的低压涡轮机叶片进行精铸并加工成最终形状。AM空气箔将需要最少的加工，这是一个优势。本文介绍了一些相对较新的进展以及与钛及其合金在航空航天部件中的生产和使用相关的一些问题和机遇。其中包括新的钛合金，钛合金的新应用以及几种制造工艺的当前状态，包括讨论增材制造的前景和现实，这是一种潜在的革命性生产钛合金部件的方法。