Abstract
This study was conducted to assess and compare the crack‐healing ability of conventional electrical sintered and microwave sintered Al2O3/x wt. % SiC (x = 5, 10, 15, and 20) structural ceramic composites. The crack‐healing ability of both conventional electrical sintered and microwave sintered specimens was studied by introducing a crack of ∼100 µm length by Vickers’s indentation and conducting a heat treatment at 1200°C for dwell time of 1 h in air. The flexural or bending strength of sintered, cracked, and crack‐healed specimens was determined by three‐point bending test, and the phase variations by X‐ray diffraction and SEM micrographs before and after crack‐healing of both the sintering methods were studied and compared. The results show that almost all the specimens recovered their strength after crack‐healing, but the strength of microwave sintered Al2O3/SiC structural ceramic composites has been shown to be better than that of conventional electrical sintered Al2O3/SiC structural ceramic composites. The microwave sintered crack‐healed Al2O3/10 wt. % SiC specimen shows higher flexural strength of 794 MPa, which was 105% when compared with conventional electrical sintered Al2O3/10 wt. % SiC and crack‐healed Al2O3/10 wt. % SiC specimen. It was found by X‐ray diffractogram that before crack‐healing, all the conventional electrical sintered samples have SiO2 phase which reduce the crack‐healing ability and microwave sintered samples with 15 and 20 wt. % SiC show lesser SiO2 phase and 5 and 10 wt. % SiC samples have no SiO2 phase before crack‐healing. However, after crack‐healing treatment, all the samples have distinct SiO2 phase along with Al2O3 and SiC phases. Microwave sintered Al2O3/10 wt. % SiC specimen cracks were fully healed which was evident in SEM micrographs.
Highlights
In recent years, more concentration has been given to the structural ceramics with exemplary mechanical, chemical, and thermal properties [1]
From the review article [23], the optimum condition for crack-healing an Al2O3/SiC ceramic composite to recover its full strength is annealing at 1200°C for 60 minutes in air. erefore, one set of cracked specimens was subjected to crack-healing treatment in an electric resistance heating furnace with MoSi2 as heating elements and another set was kept as cracked for investigation. e flexural strength of smooth, cracked, and crack-healed specimens was determined by the three-point bending test based on the ASTM C1161 standard with a support span (L) of 40 mm length with a speed of 0.5 mm/min. ree specimens were used in each condition to calculate the flexural strength
Is indicates that all specimens recovered flexural strength and showed that the cracks were healed partially or completely. e higher flexural strength of 794 MPa was obtained for microwave sintered crack-healed Al2O3/10 wt.% SiC structural ceramic composite. e flexural strength of crack-healed Al2O3/10wt. % SiC sample synthesized by the microwave sintered method was improved up to 105%, when correlated with flexural strength crack-healed Al2O3/ 10 wt. % SiC specimen synthesized by conventional electrical sintering
Summary
More concentration has been given to the structural ceramics with exemplary mechanical, chemical, and thermal properties [1]. Structural ceramics are responsive to the existence of surface cracks by reason of their brittle nature. Crack-healing nature of various ceramic composites by heat treatment was researched by the material researchers. Gupta [3] synthesized thermally shocked MgO and observed the crack-healing ability from 1400°C to 1650°C. Nakao et al [4] found excellent crack-healing ability in Al2O3/30 vol% SiC composite, mullite/15 vol% SiC composite, and Si3N4/20 vol% SiC composite when heat treated at 1200°C for 1 hour dwell in air. E cracks created by machining in Al2O3, Si3N4, and mullite ceramics reinforced with SiC could be healed at 1200°C, 1300°C, and 1300°C, respectively, with the dwell time of 1 hour in air [5]. Nam and Hwang [7] found that the optimal crack-healing condition for ZrO2/SiC was 800°C for 5 hours in air
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