چكيده به لاتين
In this study, the production of NbAl3 intermetallic based-composite with Al2O3 reinforcing particles by self-propagating high-temperature synthesis (SHS) method and in situ was investigated, during which the effect of relative green density and excess aluminum on the properties and microstructure of the composite produced was studied and evaluated. For this purpose,in first, samples prepared from the reaction materials powder, including niobium oxides and aluminum, were subjected to thermal analysis (DTA) to investigate the changes and reactions performed during the combustion synthesis process. Sample temperature changes during synthesis were recorded by non-contact digital thermometers. After combustion synthesis, phase changes by X-ray diffraction (XRD) analysis and microstructures by scanning electron microscopy (SEM) were studied. The porosity of the samples was calculated and the hardness of each sample was recorded. The effect of relative green density (three samples with relative green density of 75, 85 and 95% of the theoretical maximum density) and excess aluminum (stoichiometric sample and two samples with 20 and 40 wt% of excess aluminum) on the properties and microstructure of NbAl3-Al2O3 composite was investigated. XRD and SEM-EDS analyses showed that regardless of the relative green density and excess aluminum effect, the main phases in all samples were NbAl3 and Al2O3. Temperature changes over time during the synthesis of three samples with a relative green density of 75, 85 and 95% showed that combustion occurs faster with an increase in the relative green density. In fact, in the sample with a relative density of 75%, combustion occurred after about 95 seconds, in the sample with a relative density of 85%, occurred after 50 seconds and in the sample with 95% combustion occurred after about 46 seconds. Also, temperature changes over time during the synthesis of three samples with zero (stoichiometric sample), 20 and 40 wt% of excess aluminum showed that by increasing the amount of excess aluminum in the system, combustion is delayed. In fact, in the sample with 0 wt% of excess aluminum, combustion occurred after about 55 seconds, in the sample with 20 wt% of excess aluminum after about 65 seconds, and the sample with 40 wt% of excess aluminum combustion occurred after about 75 seconds. Recording the temperature of the samples during the synthesis of three samples with zero (with combustion temperature of 974 ° C), 20 (with combustion temperature of 965 ° C) and 40 wt% of excess aluminum (with combustion temperature of 939 ° C) showed that by increasing the amount of excess aluminum in the system, combustion temperature of the samples decreases. In microstructural analysis of all samples, Nb-rich white phase were observed, where these white phase particles in two samples with 20 and 40 wt% excess aluminum are scattered in the form of linear bands near the interface between the intermetallic and ceramic phases. In addition, Some metallic aluminum was observed in the synthesis products of two samples with 20 and 40 wt% excess aluminum. Hardness measurement showed that the presence of excess aluminum as a flexible phase caused a significant reduction in hardness values from 1017 Vickers (for sample with stoichiometric aluminum) to 136 Vickers (for sample with40 wt% excess aluminum). Evaluation the porosity percentage of all samples showed a porosity of about 22 to 33 percent.
Keywords: Combustion Synthesis ,SHS Mode, Aluminothermic, Intermetallic Based Composite, Aluminide Based Composite
