In situ reaction mechanism of MgAlON in Al–Al2O3–MgO composites at 1700°C under flowing N2

The Al–AlO–MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M, M, and M, respectively, were prepared at 1700°C for 5 h under a flowing Natmosphere using the reaction sintering method. After sintering, the Al–AlO–MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen Mwas composed of MgO and MgAlO. Compared with specimen M, specimens Mand Mpossessed MgAlON, and its production increased with increasing aluminum addition. Under an Natmosphere, MgO, AlO, and Al in the matrix of specimens Mand Mreacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al–AlO–MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an Natmosphere, the partial pressure of oxygen is quite low; thus, when the Al–AlO–MgO composites were soaked at 580°C for an extended period, aluminum metal was transformed into AlN. With increasing temperature, AlOdiffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with AlOto form MgAlO. When the temperature was greater than(1640 ± 10)°C, AlN diffused into AlOand formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and Mg AlOat high temperatures because of their similar spinel structures.

Extraction of the dynamic plastic behavior of AlON single crystals by nanoimpact

Investigating the dynamic mechanical behavior of single-crystal aluminum oxynitride(AlON)is fascinating and crucial for understanding material performance in relevant applications.Nevertheless,few studies have explored the dynamic mechanical properties of AlON single crystals.In this study,a series of nanoimpact experiments(representative strain rateε˙r≈102s^(-1))were performed on three principal orientations((010),(101),and(111))of grains to extract the dynamic mechanical responses of AlON single crystals.Our results reveal that the dynamic plasticity of an AlON single crystal is governed by a combination of mechanisms,including dislocation motion and amorphization.Significantly,the localized amorphization induced by mechanical deformation has a softening effect(a lower dynamic hardness).The crystallographic orientation affects the dynamic hardness similarly to the static hardness.In particular,the(111)orientation results in the highest hardness,whereas the(010)orientation is the softest among the three principal orientations.This dependency aligns with the expectations derived from applying Schmid law.Furthermore,both the dynamic and static hardnesses exhibit typical indentation size effects(ISEs),which can be effectively described via the strain gradient theory associated with the geometrically necessary dislocations.In addition,the size and rate dependencies of the dynamic hardness can be decoupled into two independent terms.

Novel synthesis of fine γ-AlON powders from the hydrolysis of Al metal

In this study, fine aluminum oxynitride (γ-AlON) powder was synthesized from a solid-state hydrolysis byproduct for the first time through in-depth research on the hydrolysis of metal Al powder. Hydrolysis begins on the surface of the Al particles, the initial solid-state hydrolysis byproduct is AlOOH and then Al(OH)_(3), and during the reaction stage, a unique core‒shell structure with a hollow outer core composite precursor is formed. Pure-phase AlON powder can be synthesized by utilizing a composite precursor with an appropriate Al_(2)O_(3)/Al ratio (Al_(2)O_(3)/Al = 10.27) under a flowing N_(2) atmosphere. The core‒shell structure decreases the diffusion distance between raw materials and reduces the nitridation temperature (1700 °C). Furthermore, the unique hollow structure of the composite precursor results in some of the synthesized AlON powder also having a hollow structure, which is conducive to powder crushing, and fine nanoscale (D50 = 292 nm) powder can be obtained only via a grinding process. The combination of Al–H_(2)O reaction and direct nitridation (DN) methods has led to the development of a new synthesis method for AlON powder and provides a new method for the recovery of the solid-state hydrolysis byproduct of metal Al powder.

Synthesis of polycrystalline γ-AlON powders by novel wet chemical processing

The synthesis of polycrystalline aluminum oxynitride （AlON） powders was investigated by the carbothermal reduction and ni- tridation （CRN） of amorphous precursor obtained by wet chemical processing. Co-precipitation processing was employed to achieve amorphous precursor from AI（NO3）3 solution dispersed by nanosized carbon particles, which was composed of AI（OH）3 and C particles homogeneously. The effects of the content of carbon black, pH value, and calcination temperature on formation of A1ON phase were investigated by means of XRD, SEM and TEM, respectively. It was found that single phase AION powder could be synthesized when the resultant precursors were calcined at 1750℃ for 2 hours under flowing N2. Un- der optimal additional content of C （5.6wt%）, the resultant A1ON powders exhibited the primary particle size of about 1-3 μm with a specific surface area of 3.2 m2/g, which were superior to that of carbothermal reduction of immediate mixture of γ-A1203/C powders.