Microstructure modification of Y2O3 stabilized ZrO2 thermal barrier coatings by laser glazing and the effects on the hot corrosion resistance

Y2O3 stabilized ZrO2(YSZ)thermal barrier coatings(TBCs)are prone to hot corrosion by molten salts.In this study,the microstructure of atmospheric plasma spraying YSZ TBCs is modified by laser glazing in order to improve the corrosion resistance.By optimizing the laser parameters,a^18μm smooth glazed layer with some vertical cracks was produced on the coating surfaces.The as-sprayed and modified coatings were both exposed to hot corrosion tests at 700 and 1000℃for 4 h in V2O5 molten salt,and the results revealed that the modified one had improved corrosion resistance.After hot corrosion,the glazed layer kept structural integrity,with little evidence of dissolution.However,the vertical cracks in the glazed layer acted as the paths for molten salt penetration,accelerating the corrosion of the non-modified coating.Further optimization of the glazed layer is needed in the future work.

Effects of Mierostructure Modification on Properties of MN/BN Composites

It is very difficult to prepare full-densified aluminum nitride-boron nitride （AIN/BN） composite ceramics with homogeneous microstructure and high thermal conductivity. Spark plasma sintering （SPS） was used to fully densify the AIN/BN composites in this work. Microstructure, mechanical properties and thermal conductivity of the SPS sintered AIN/BN composites with 5-30 vol% BN were investigated. The results show that the microstructure of composites is fine and homogenous, and the AIN/BN composites exhibit high mechanical properties. To promote the growth of AIN grains and modify the distribution of grain boundary in AIN/BN composites, a heat treating methodology was introduced through gas pressure sintering （GPS）. This processing was significantly beneficial to enhancing the thermal conductivity of the specimen. The thermal conductivity of AIN/BN composites with 5-30 vol% BN reached 60 W/m K after the samples were treated by GPS.

A review of classical hydrogen isotopes storage materials

Hydrogen storage alloys(HSAs)are attracting widespread interest in the nuclear industry because of the generation of stable metal hydrides after tritium absorption,thus effectively preventing the leakage of radioactive tritium.Commonly used HSAs in the hydrogen isotopes field are Zr2M(M=Co,Ni,Fe)alloys,metallic Pd,depleted U,and ZrCo alloy.Specifically,Zr2M(M=Co,Ni,Fe)alloys are considered promising tritium-getter materials,and metallic Pd is utilized to separate and purify hydrogen isotopes.Furthermore,depleted U and ZrCo alloy are well suited for storing and delivering hydrogen isotopes.Notably,all the aforementioned HSAs need to modulate their hydrogen storage properties for complex operating conditions.In this review,we present a comprehensive overview of the reported modification methods applied to the above alloys.Alloying is an effective amelioration method that mainly modulates the properties of HSAs by altering their local geometrical/electronic structures.Besides,microstructural modifications such as nano-sizing and nanopores have been used to increase the specific surface area and active sites of metallic Pd and ZrCo alloys for enhancing de-/hydrogenation kinetics.The combination of metallic Pd with support materials can significantly reduce the cost and enhance the pulverization resistance.Moreover,the poisoning resistance of ZrCo alloy is improved by constructing active surfaces with selective permeability.Overall,the review is constructive for better understanding the properties and mechanisms of hydrogen isotope storage alloys and provides effective guidance for future modification research.

Effect of combinative addition of mischmetal and titanium on the microstructure and mechanical properties of hypoeutectic Al-Si alloys used for brazing and/or welding consumables

Effects of mischmetal（RE） and/or Ti modifier on the microstructure including α-Al dendrites, eutectic Si phases and other secondary phases of Al-Si brazing and/or welding alloys were investigated by differential scanning calorimetry（DSC）, optical microscopy（OM）, scanning electron microscopy（SEM）. The DSC results showed that an addition of RE decreased the eutectic temperature and caused supercooling, promoting the nucleation of eutectic Si crystals. In addition, the maximum temperature of the first endothermic peak varied with the different RE contents, which had a good correlation with the microstructural modification of the eutectic Si phase. The α-Al dendrites were well refined by increasing the cooling rate or adding 0.08 wt.% of Ti. When 0.05 wt.% RE was added to the Al-5Si-0.08 Ti alloy, the morphology of eutectic Si phase was transformed from coarse platelet to fine fibers and the mechanical properties of the resulting welding rod were well improved. Whereas, when excess RE was added, a large number of β-Fe phases appeared and the aspect ratios of β-Fe phases increased. The morphologies and chemical components of two kinds of RE-containing intermetallic compounds（IMCs） were also discussed.

Generic principles of crack-healing ceramics

Ceramic materials able to heal manufacture or damage induced microstructure defects might trigger a change in paradigm for design and application of load bearing ceramics.This work reviews thermodynamic and kinetic aspects governing the regeneration of solid contact able to transfer stress between disrupted crack surfaces in ceramics.Major crack healing processes include perturbation of crack-like pores followed by sintering of isolated pores,as well as reaction with an environmental atmosphere and filling of the crack space with an oxidation product.Since thermally activated solid state reactions require elevated temperatures which may exceed 1000℃,processes able to trigger crack healing at lower temperatures are of particular interest for transferring into engineering applications.Generic principles of microstructure modifications able to facilitate crack repair at lower temperatures will be considered:(i)acceleration of material transport by grain boundary decoration and grain size reduction,and(ii)reduction of thermal activation barrier by repair filler activation.Examples demonstrating crack healing capability include oxidation reaction of low energy bonded intercalation metal from nano-laminate MAX phases and catalyzed surface nitridation of polymer derived ceramics containing repair fillers.

Heterogeneous particle structure formation during post-crystallization of spray-dried powder

The formation of heterogeneous particle structure in skim milk powder has been investigated in a post- crystallization facility using experimental and a mathematical model. Various processing conditions were used to produce these heterogeneous structures. The experimental process parameters were used as initial and boundary conditions for the model. The modelled data agreed well with the experimental data. The experimental and modelling results show that the powder processed at high water activity （aw = 0.7） with low initial moisture content （X0 = 0.01 kg/kg） developed a crystalline surface layer while the core of the particle remained amorphous. This structure is referred to as an egg-shell structure. The powder that was processed at low water activity （αw = 0.1） with high initial moisture content （X0 = 0.2 kg/kg） developed a crystalline core while the surface of the particle remained amorphous. This structure is referred to as an egg-yolk structure. Understanding the dependency of particle microstructures on the processing conditions could be useful when developing procedures to control the drying equipment because the particle microstructure affects the physicochemical properties of the powder and potential applications and behaviour of the powder.