钛合金/钢异种材料熔化焊研究现状

Research Status for the Fusion Welding Between Titanium Alloy and Steel

钛合金具有比强度高、耐腐蚀和耐高温等优点,但其推广应用受限于高制造成本。而钢是应用最广泛的传统结构材料,具有制造成本低、力学性能优异等优点,但其具有高温可靠性且耐蚀性较差、密度比较大。钛合金/钢异种材料的高可靠性连接能充分发挥两种材料在性能和经济上的优势互补,在航空航天、能源化工、海洋装备和医疗器械等诸多领域具有广阔的应用前景。因此,开展钛合金与钢连接方面的研究工作具有重大意义。钛合金和钢在物理化学性能方面的差异导致二者连接过程中存在诸多问题,主要集中于以下两个方面:(1)残余应力大。由于热膨胀系数的差异性,钛合金/钢异质材料连接接头会产生较大的残余应力,严重影响连接接头的可靠性。(2)脆性金属间化合物的形成。室温下,Fe在Ti中的固溶度极小(仅为0.05%~0.1%),而在钛合金/钢连接接头中容易形成一系列Fe-Ti脆性金属间化合物,造成接头脆化、韧性降低甚至开裂。近年来,研究人员通过改变连接工艺和制备合金化焊料等措施调控脆性金属间化合物的形成,改善接头的可靠性,取得了一些突破性进展。在诸多连接方法中,熔化焊方法具有焊前准备简单、生产效率高和连接件尺寸外形限制少等特点,是实现钛合金/钢异质金属高可靠性连接的主要焊接方式。本文总结了近年来采用熔化焊方法实现钛合金/钢连接的国内外研究成果,探讨了中间层种类、焊接参数对接头微观组织演变和力学性能变化的影响规律,讨论了钛合金/钢连接技术存在的问题,以期为钛合金/钢连接领域的研究和技术发展提供理论依据及技术参考。

Titanium alloy has the advantages of high specific strength,corrosion resistance and high temperature resistance,but the widespread application of titanium alloy is restricted by its high manufacturing cost.Steel is the most widely-used traditional structural material,owing to its low manufacturing cost and excellent mechanical properties,but it has high temperature dependence,poor corrosion resistance,and relatively high density.On account of their complementary properties,combining titanium alloy with steel is ideal for the fabrication of materials with broad application prospects in the fields of aerospace engineering,energy and chemical industries,marine equipment,and medical equipment.Consequently,it is of great significance to study the mechanism involved in combining titanium alloy and steel.Due to the differences in physical and chemical properties between titanium alloy and steel,many issues arise during the combination process.The two main issues are as below:(Ⅰ)large residual stress due to the difference in thermal expansion coefficient and the combination of two dissimilar materials,which seriously affects the robustness of the connection joint;(Ⅱ)the formation of brittle intermetallic compounds,which means that a series of Fe-Ti brittle intermetallics are likely formed in titanium alloy/steel joints,with the extremely poor solid solubility of Fe in Ti(only 0.05%to 0.1%)at room temperature,leading to embrittlement,toughness reduction and even cracking of the connection joint.In recent years,some breakthroughs in regulating the formation of brittle intermetallics and improving the reliability of joints have been obtained by altering the combination process and preparation of alloyed filler metals.Among many methods for combining the two materials,fusion welding has the beneficial characteristics of simple pre-weld preparation,high production efficiency and less size limitation of the connecting parts;thus,it is the main welding method used for achieving a highly reliable connection of titanium alloy with steel.The domestic and foreign research results of titanium alloy/steel welded joints by fusion welding method in recent years are summarized,along with the effect law of intermediate layer types and welding parameters on the evolution of microstructure and mechanical properties of the welded joints.Additionally,the problems of titanium alloy/steel connection technology are explored.The main purpose of this review is to provide a technical reference and theoretical basis for research and technological development in the fields of employing titanium alloy/steel connections.