Low carbon steels have been joined using an infrared processing technique with copper as the filler material. Single lap specimens were prepared. The joining temperatures were 1100 ЊC, 1125 ЊC, and 1150 ЊC with joining time ranging from 0 to 2 minutes in flowing argon. Excellent wetting between the base materials and the filler was observed for all samples. The joint shear strength was determined with a specially designed fixture to minimize the bending moment of specimens during testing. The measured joint shear strength varies from 240 to 300 MPa depending on the processing conditions. The maximum strength obtained is about 300 MPa, which can be achieved by processing at 1125 ЊC for 60 seconds or 1150 ЊC for only 30 seconds. Higher processing temperatures or longer processing time than these conditions did not improve the joint strength. Joint cross-section examinations revealed that there are no voids in the joint. Microhardness tests performed on the cross sections of joined samples across the joint zone indicate that the joint zone hardness is higher than that of pure copper. Examinations with energy dispersive analysis of X-ray revealed presence of iron in the joint as well as a small amount of copper inside the base materials.
Chromium and chromium nitride coatings on steels have been prepared with pulsed dc magnetron sputter deposition at a frequency of 185 kHz and a duty cycle of 96%. The coating process was carried out at 150 W with the substrate temperature maintained at 200°C. For nitride coatings, reactive sputter deposition was carried out in Ar with 3, 5, or 7%N2. Heat treatments were performed for coated steels with an infrared (IR) processing technique in an attempt to modify the interfaces and change coating properties. T he heat treatment was carried out at 400°C for 2 and 5 min. Characterisation of coated samples included X-ray diffraction (XRD), optical microscopy, and microhardness tests to verify the effect of the heat treatment. Results from XRD analysis indicated that IR heat treatment at 400°C for 2 or 5 min did not change the phases present in the coatings. Optical images of the coating microstructure show that cracks were developed on coatings deposited under 7%N2 even after only 2 min heat treatment at 400°C. Severity of cracking is reduced for coatings deposited under low nitrogen contents. No cracks were observed on coatings deposited without nitrogen. Microhardness measurements showed that for all coated specimens, 2 min IR treatment at 400°C gave the highest microhardness. For samples treated for 5 min, the microhardness decreased. X-ray diffraction analysis with slow scanning showed that CrN peaks were developed in the coatings deposited under 7%N2 and heat treated at 400°C for 2 and 5 min.
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