Strength recovery of machined Al₂O₃/SiC composite ceramics by crack healing

Abstract

A B S T R A C T Alumina is used in various fields as a machine component. However, it has a low fracture toughness, which is a weakness. Thus, countless cracks may be initiated randomly by machining, and these cracks decrease the component's mechanical properties and reliability.To overcome this problem, a crack-healing ability could be a very useful technology. In this study, Al 2 O 3 /SiC composite was sintered. This alumina exhibits excellent crackhealing ability. Small specimens for a bending test were made from the Al 2 O 3 /SiC. A semicircular groove was machined using a diamond ball-drill. The machining reduced the local fracture stress from approximately 820-300 MPa. The machined specimens were crack-healed under various conditions. The fracture stress of these specimens after crack healing was evaluated systematically from room temperature (RT) to 1573 K. It was found that the local fracture stress of the machined specimen recovered almost completely after crack healing. Therefore, it was concluded that crack healing could be an effective method for improving the structural integrity of machined alumina and reducing machining costs.

Crack Healing of Machining Cracks Introduced by Wheel Grinding and Resultant High‐Temperature Mechanical Properties in a Si3N4/SiC Composite

“…In response to crack‐healing treatment at 1400°C for 10 h, the machined specimens exhibited the same strength as the nonmachined specimens. Similar behavior has been observed in Al 2 O 3 /SiC 9,10 and Mullite/SiC 8 composites. These results indicate that crack‐healing treatment is the most effective method for increasing reliability and is the best substitution for costly precision machining processes.…”

“…To overcome this problem, many researchers have studied the relationship between machining conditions and damage to identify the optimized machining condition that introduces only acceptable surface damages 2,3,6 . Alternatively, some researchers have attempted to develop more economical means of self‐crack‐healing for machining damage 7–10 …”

A review of some of experimental and numerical studies of self‐crack‐healing in ceramics

“…The oxidation products were Ti 2 AlC and Ti 2 SnC. The crack-healing behavior of Al 2 O 3 / SiC composite was investigated under various conditions by Ono et al 48 The healing process was accomplished through the sintering of the composites. The heat treatment conditions to heal the cracks completely ranged from (1000°C-1400°C) in air.…”

“…Systems like Si 3 N 4 /SiC, Mullite/SiC, and Al 2 O 3 / SiC have been investigated and showed significant selfhealing abilities. 19,48,55 The crack-healing behavior in Al 2 O 3 was investigated by Kim et al 56 Their results showed that cracks can be healed by sintering the samples above 1400°Ϲ for 1 hour. The crack-healing behavior of Cr 2 AlC ceramic as a function of temperature, time, and crack size was investigated by Li et al 57 In their study they showed that healing of the cracks was due to annealing of the specimens at temperatures above 1000°C.…”

Crack healing and strength recovery in SiC/spinel nanocomposite

“…On the other hand, numerous studies reported the effectiveness of SiC particles as a healing agent. Some of the common composites are SiC/ Al 2 O 3 [16], SiC/Si 3 N 4 [17], SiC/ZrB 2 [18] and SiC/Al 6 Si 2 O 13 [19], to name a few. At high enough temperature, SiC reacts with oxygen and produce SiO 2 which is accompanied with almost 81% volume expansion.…”