PSI - Issue 2_A

Dariusz Boroński et al. / Procedia Structural Integrity 2 (2016) 3764 – 3771 Boro ń ski et al./ Structural Integrity Procedia 00 (2016) 000–000

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1. Introduction Construction materials applied in aviation and aerospace industries must meet numerous requirements connected with specific service conditions under which they are used. Thus providing these structures with adequate mechanical properties, with possibly low density, is of key importance. Additionally, it is necessary to maintain the required mechanical properties in changeable environments, in particular, in significantly different temperatures. Materials used in coatings of objects operating in outer space need to have proper ballistic resistance and radiation hardness. Meeting these requirements for homogenous materials is not easy, hence new solutions are being sought. The layered material Al/Ti discussed in this study which is obtained with the used of explosive welding is an example of such a material. Literature analysis shows significant interest in composite materials constructed on the basis of aluminum and titanium. Most works are dedicated to analysis of mechanical properties and analysis of the joint zone microstructure. For example, Fan et al. (2016) have studied the influence of thickness of particular layers of steel sheets consisting of aluminum AA1060 with titanium alloy explosion welded on selected mechanical properties has been studied. Also drawabilty of the considered material has been tested after the welding process. Apart from that, the impact of the number of layers on selected mechanical properties have been studied. Szachogluchowicz et al. (2015) have reported the results of tests of low cycle fatigue life of an explosion welded aluminum AA2519 and Ti6Al4V alloy composite. Fronczek et al. (2016) have compared local properties, in particular, the percentage share of particular components making up a plated coating, in the transition zone between the aluminum and titanium layers. In this work there are results of comparative studies of the microstructure and micro hardness of the plated coating components measured directly after explosion welding and the process of annealing. It is much more difficult to find tests results of Al/Ti composites for reduced temperatures. However, it is possible to find tests results for homogenous materials. For example, this type of tests were reported by Nayana et al. (2014). The paper contains results of tests of selected mechanical properties for specimens of AA2195 aluminum bathed in liquid nitrogen. The authors have also carried out an analysis of the tested specimens fracture surface microstructures. Numerous works are devoted to an analysis of transition zones between the connected materials and their influence on mechanical properties of a layered material. For instance, Bataev et al. (2012), Rohatgi et al. (2003), Jiang et al. (2013), Xu et al. (2006) have presented an analysis of the influence of Al 3 Ti intermetallic diffusion on the structure of Al/Ti composite. The influence on local reinforcements of the material has been shown as well as the possibility of providing the material with discontinuity and predisposition to delamination. They can also be viewed as inclusions, which cause undesired stress and strain concentration, especially in the case of time variable loads. Also the influence of heat treatment has been widely analyzed including procedures involving modification of the residual stress state. Results of this type of tests are also described by Luo and Acoff (2004), Peng et al. (2005). The literature analysis proves that there are no thorough analyses of Al/Ti composite behavior in significantly reduced temperatures which is necessary to know if they are to be used in aviation industry, in particular, in objects which operate in outer space. One of the most important properties affecting safety of mechanical structures operation is fracture toughness of materials used in them. The goal of this study is to present a comparative analysis of Al/Ti composite crack resistance in the ambient temperature and cryogenic conditions. Procedures used in the tests have been described and tests results obtained for temperatures 293 K and 77 K have been presented. 2. Research object The research object is depicted in Figure 1a. It is an explosion welded layered material made of two alloys: aluminum AA2519 and titanium Ti6A14V (Fig.1b). The main mechanical properties of the used materials are presented in Table 2. The aluminum alloy, before welding, undergoes heat treatment and additional layer of aluminum AA1050 in the form of a diffuser plate or plated coating is inserted into the weld zone. After welding it is subjected to heat treatment again. The weld zone is characterized by high complexity in terms of geometry,