Microstructure Changes and Phase Growth Occurring

Authors: D M Fronczek R Chulist L LitynskaDobrzynska Z Szulc P Zieba J WojewodaBudka

Publish Date: 2016/03/04

Volume: 25, Issue: 8, Pages: 3211-3217

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Abstract

The manuscript presents a close examination of the titanium and aluminum platters manufactured by explosive welding method In particular the microstructure changes of the Al/Ti wavy shape interface after annealing at 773 and 903 K were studied Three stable TiAl3 TiAl and Ti3Al and a metastable TiAl2 intermetallic phases have been formed in the state directly after explosive welding The orientation map and TEM images obtained after explosive welding process showed very fine grains of aluminum mixed with intermetallics in the interface region between the peninsulas or islands After annealing for 100 h the TiAl3 continuous layer was obtained however the layer achieved at 903 K was much wider than that obtained at 773 K An examination of the growth kinetics at 903 K revealed that incubation time was less than 5 min After this period the growth was solely governed by chemical reactionThis article is an invited submission to JMEP selected from presentations at the Symposium “Joining Technologies” belonging to the Topic “Joining and Interfaces” at the European Congress and Exhibition on Advanced Materials and Processes EUROMAT 2015 held September 2024 2015 in Warsaw Poland and has been expanded from the original presentationDifficulties associated with joining of dissimilar metals or alloys by conventional fusion joining methods are mostly related to difference in melting temperature brittle phase formation and internal stresses This leads to a weak joint and makes the weld too brittle Ref 1 2 A way of overcoming this problem is to employ solidstate joining processes One of the solidstate joining techniques for obtaining reliable joints between dissimilar materials is explosive welding method EXW In this process the energy comes from the explosion of explosive materials and the pressure of the flyer plate is propelled toward the base plate Ref 3 4 The main advantage of EXW is related to the ability of joining various shapes such as plate to plate Ref 5 or tube to sleeve Ref 4 and also it provides a high purity of the interface The EXW technique is referred to the cold techniques where the high temperature appears only locally Ref 6 As a result of such a method different intermetallic phases at the interface can be formed for example TiAl3 in titaniumaluminum Ref 7 FeAl3 in aluminumsteel Ref 8 and CuAl2 in copperaluminum Ref 9 10TiAl phase diagram consists of three stable intermetallics Ti3Al TiAl and TiAl3 and one metastable TiAl2 phase Ref 11 The TiAl3 phase is the most predicted one because its formation is thermodynamically and kinetically favored For instance only this intermetallic phase TiAl3 formed at the interface after the diffusion bonding of Ti and Al plates in Ref 12 13 TiAl3 with Young’s modulus equal to 216 GPa higher oxidation resistance and lower density 33 g/cm3 is more expected than the other titanium aluminides Ref 14 However as solidification process during EXW goes far from the equilibrium conditions the presence of another phases cannot be excluded Ref 10Formation of the continuous layer of intermetallics is necessary in the metallicintermetallic laminate MIL production These materials are characterized by special mechanical properties due to their micro meso and macrostructure Therefore they can be applied in aerospace or chemical industry Ref 7 15 Even if the continuous layer is not created in the state directly after explosion which is often the case further annealing allows to obtain a desired structure Ref 7There are few reports concerning the EXW of Ti and Al For example ten plates of titanium and eleven plates of aluminum were explosively welded by Bataev et al Ref 6 In order to obtain a continuous intermetallic layer the clads were annealed under the air atmosphere for various periods of time from 1 to 100 h at 903 K MIL composites composed of Ti/TiAl3/Al were analyzed in detail concerning their microstructure and mechanical properties In Foadian et al’s Ref 16 17 experiment three titanium and three aluminum clads were successfully welded The influence of temperature on the TiAl3 phase growth during annealing for various times from 1 to 70 h Ref 16 and 1 to 260 h Ref 17 at 903 K under ambient atmosphere was examined too In study of Pavliukova et al Ref 18 ten titanium sheets with nine aluminum sheets were joined using the EXW method and further annealed for 40 h at 913 K with or without external pressure of 12 MPa Once again the TiAl3 phase was the only one which was present in the interconnection area Despite the fact that the Al/Ti explosively welded joints are commonly described in the literature a detailed qualitative and quantitative analysis of their interfaces has not been performed so far The presence of other than TiAl3 intermetallic phases was not taken into consideration as wellTherefore the main aim of the present study of the titaniumaluminum explosively welded samples was to investigate the microstructure and phase composition close to the interface as well as to compare the growth rate of the intermetallic phase under various temperatures 903 825 and 773 K and under vacuum atmosphere This allows calculation of the kinetics of intermetallic growth and also answer the question what mechanisms govern the growth at given temperature of annealingAluminum A1050 coldrolled sheet with dimensions of 460 mm long 140 mm wide and 4 mm thick and titanium Ti Gr 2 coldrolled sheet with dimensions of 460 mm long 140 mm wide and 08 mm thick were used as the base plate and flyer plate respectively They were separated by a standoff distance equal to 15 mm An explosive material ANFO was placed on top of the flyer plate The detonator was placed near the edge in the middle of the plate width The detonation velocity during explosion was 1900 to 1950 m/s and the jetting direction was parallel to the rolling direction RD

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