Heat treatment is an important processing procedure for single metal materials to obtain a certain structure and performance, and it is also an important processing procedure for metal explosive composite materials to obtain a certain structure and performance. The heat treatment types of this kind of materials also include annealing, quenching, tempering, normalizing and aging. This article takes the annealing of several explosive composite panels as an example to discuss the related issues.
1 Test materials
The following explosive clad plates were used in this test: titanium-steel, stainless steel-steel, nickel-titanium, nickel-stainless steel, copper-aluminum, copper-LY12, copper-LY2M and zirconium-steel.
2 Test method
The blanks of the explosive composite board samples were annealed and heat treated according to the process shown in Table 1. Then carry out the following work:
(1) A part of the above-mentioned blank is made into metallographic samples by explosive welding metallographic technology, and the microstructure of the bonding zone of the composite plate under different annealing processes is observed under a metallographic microscope, and the corresponding metallographic photos are taken.
(2) Use the above-mentioned titanium-steel, stainless steel-steel, nickel-titanium and nickel-stainless steel composite plate blanks to make shear specimens, test their shear strength on a universal material testing machine, and plot these data in different annealing processes The change curve under.
(3) Using metallographic samples of titanium-steel, stainless steel-steel, nickel-titanium and nickel-stainless steel composite plates, measure the microhardness on the microhardness tester according to the predetermined procedures and methods, and draw the bonding area of the corresponding materials Microhardness distribution curve.
3.1 The bonding zone organization of the composite board
It can be seen from Figure 1 that the microscopic morphology of the bonding zone of the titanium-steel composite plate has undergone significant changes after annealing. Figure 1a shows the structure of the explosion state before annealing. It can be seen from this figure that the bonding interface is a wave shape. This wave interface is unique to the transition zone of explosively welded composite materials. It can also be seen from the figure that two different forms of plastic deformation structures appear on both sides of the wave interface. On the steel side, this deformation is manifested by the elongated crystal grains, just like the deformed fibers in the conventional rolling process. Moreover, the degree of deformation is the most serious near the interface, and the degree of deformation decreases as the distance from the interface increases. The original structure of steel appears below the waveform, and some twin crystals can also be seen. Under high magnification, sub-grains and equiaxed grains similar to recrystallization can be observed on the interface. On the titanium side, the deformation of the metal appears in the form of “flying lines” flying from the interface into the titanium. This kind of flying line is adiabatic shear line, which is essentially a special form of plastic deformation line . There are more twin crystals in titanium than steel. There is a vortex area in the wave front, where most of the molten metal formed during the explosive welding process is gathered, a small amount of which is distributed on the wave ridge, and its thickness is measured in μm. The bonding zone with such characteristics is the welding transition zone of explosive welding metal composite materials.
After annealing, many changes have taken place in the microstructure in the bonding zone: the flying lines on the titanium side disappeared at 500°C, the titanium began to recrystallize, and the deformed streamlines on the steel side remained (Figure 1b). The grains of annealed titanium at 600°C are growing; although there are still deformed streamlines in some places on the steel side, most of them also begin to recrystallize, and the amount of pearlite decreases (Figure 1c). When annealing at 700°C, the deformed structure in the steel disappears completely, the pearlite also disappears, and the grains are growing; the grains of titanium grow larger (Figure 1d). The crystal grains of titanium and steel are still growing after annealing at 800 and 850°C. At this time, an intermittent cluster of new phase regions appear at their interface (Figure 1e, f). At 900°C, the new phase zone has been connected into a band (Figure 1g). At this time, due to the diffusion of iron in the steel to the titanium side, the α→β phase transition temperature of titanium is increased, that is, the phase transition has not yet occurred at this temperature (the phase transition temperature is 882°C). When the temperature rises to 1000°C, the titanium side changes from α-Ti to β-Ti. In addition, due to the diffusion of iron, carbon and titanium through the interface, several distinct organizational morphologies appear on the interface and on both sides (Figure 1h), that is, an intermediate layer containing a large amount of intermetallic compounds.