چكيده به لاتين
The purpose of this study is to evaluate the connection of WC-8Co tungsten carbide to VCN-150 steel using combustion synthesis reactions and to investigate the degree of adhesion and strength of the connection and also the factors affecting this process. A laboratory-scale setup was designed and built for joining two cylindrical pieces of steel and tungsten carbide through an intermediate reactive compact made from Ni+Ti powder mixture. The designed setup made possible the applying of an axial pressure during heating the samples as well as providing a protective atmosphere for the exothermic reaction between Ni and Ti. Once the nickel-titanium compressed samples were subjected to a high heating rate by an induction furnace in an argon atmosphere, the liberated heat due to the exothermic reaction between these two and the formation of NiTi intermetallic compound thereof was sufficient for the joining of the produced NiTi to both steel and carbide. The effect of the particle sizes of nickel and titanium, the applied force, and the thickness of the bonding layer on the joining process, interdiffusion of elements, volume of porosity, ignition time, and finally the shear strength of the produced interface was evaluated. After the joining process, the samples were cut in halves and the cross-section was prepared for studying the microstructural features as well as bonding quality. In order to characterize the joined samples, X-ray diffraction (XRD) and scanning electron microscopy along with energy dispersive spectroscopy (SEM-EDS) techniques were used. The average shear strength of each sample was measured using a shear-evaluation system designed and fabricated according to ASTM standard. Analyses confirmed the formation of NiTi as the main phase due to the combustion synthesis reaction in the compressed powder mixture of Ni + Ti (bonding layer). The results showed that by reducing the average particle size of nickel from 62 to 3 microns, due to increasing the contact surfaces of the powders, the ignition time of the connecting layer was reduced from 238 to 35 seconds and its reaction was more intense and hot. It was more penetrating between the components of the connection. Also, the measured shear strength increased from about zero to 32.44 MPa due to better fineness and penetration. The degree of porosity also decreased from about 20 to 4 percent. Similar results were obtained for titanium particles. Increasing the thickness of the bonding layer from 2 to 5 mm increased the porosity in the bonding layer from about 4 to 21%, reducing the shear strength from 32.44 to 7.04 MPa and reducing the mutual penetration of the elements related to the connection components. The ignition time was probably reduced from 37 to 30 seconds due to the increase in heat transfer surface as a result of the increase in the thickness of the connection layer. Increasing the applied force during the connection from zero to 60 kg with the size of the fixed particles of nickel and titanium of 3 and 30 microns, respectively, and the height of the tablet 2 mm, was the optimal connection conditions in this project. This improved the penetration of the elements in the joint of the joints and reduced the porosity in the joint layer from about 54 to 3%. The average shear strength also increased from about zero to 38.36 MPa.
Keywords: Tungsten carbide-Steel joints, Combustion Synthesis, Thermal Reaction, NiTi Intermetallic Compounds, Scanning Electron Microscope (SEM), X-ray Distribution (XRD), Shear Strength
