The influence of the shock-compressed gas composition in the gap between metal plates on the processes occurring before contact point during explosion welding

Abstract

This study examines how the material of explosion-welded plates and the composition of shock-compressed gas (SCG) in the gap between them influence the preheating of plate surfaces before impact. A series of explosion welding experiments were performed using copper plates (in air, helium, and argon) and titanium plates (in air and argon) with lengths of 0.6 and 1 m, respectively. Low-inertia planar copper–constantan thermocouple sensors were placed in the gap to record the time-dependent temperature changes at the "hot" sensor junctions. Based on the obtained temperature curves, the numerical solution of the inverse problem of thermal conductivity was applied to reconstruct the heat fluxes from the SCG acting on the plate surfaces during the entire exposure period. Targets placed in the gap between the plates allowed for the investigation of cumulative processes during oblique plate collisions, as well as the analysis of metal particle distribution formed by the dispersed cumulative jet along the gap length. It was determined that the size of the SCG region and the distribution of heat flux power along its length were influenced by the density of both the gas and the dispersed metal particles, as well as the particle concentration along the length of the SCG. During the explosion welding of copper plates in helium and air, the particles are evenly distributed along the gap, with heat fluxes of 0.3 and 0.4 GW/m², respectively. However, when the medium is replaced with argon, the denser medium causes deceleration, leading to a redistribution of copper particles along the SCG region. These particles concentrate near the point of impact, resulting in a peak heat flux of approximately 1.8 GW/m². In the rest of the SCG, the heat flux remains at 0.2 GW/m². In this case, the shock wave front velocity in air, helium, and argon is the same, equal to 1.3 times the collision velocity (V_c). When welding titanium plates, the braking effect of the light, dispersed titanium particles, and their accumulation in the impact area are noticeable in the air and reach their maximum in argon. This leads to an increase in peak heat flux values to 1.0 and 3.6 GW/m², respectively. The average heat flux in the rest of the SCG is 0.3 GW/m² for both air and argon. Additionally, when switching from air to argon, the shock wave front velocity decreases from 1.3 to 1.1 times the V_c. The SCG heat exchange process with the surface of the plates was analyzed using numerical modeling, providing the temperature values of the surface layers before impact. The results show that when welding copper in air, helium, and argon environments, the surface temperature reaches 50–180 °C. In contrast, when welding titanium in an argon environment, the surface temperature can reach the melting point of titanium.