D. Gan

The effects of TiO2 addition on the microstructure and transformation of ZrO2 with 3 and 6 mol.% Y2O3

Abstract Up to 30 mol.% TiO2 was added to ZrO2 with 3 and 6 mol.% Y2O3 and sintered in air at 1600°C for 4 h. The contents and lattice parameters of cubic (c-) and tetragonal (t-) ZrO2 were determined by X-ray diffraction. The solution of TiO2 is found to stabilize the t-ZrO2 phase but destabilize the c-ZrO2 phase. The solubility of TiO2 in t-ZrO2 in ZrO2-3mol.%Y2O3 is about 14–16 mol.% and in c-ZrO2 in ZrO2-6mol.%Y2O3 is about 18 mol.% at 1600°C. The grain size of both c- and t-ZrO2 increases with TiO2 addition. The Ms temperature of the tetragonal-to-monoclinic ZrO2 martensitic transformation was lowered by TiO2 by a cold stage study.

Mechanical properties of Fe30Mn10Al1C1Si alloy

Abstract The present work is a study of the tensile properties from 77 to 1123 K and the impact toughness from 77 K to room temperature of an austenitic Fe30Mn10Al1C1Si alloy. It was found that for temperatures below 773 K this alloy possesses high strength and good ductility, but exhibits a ductile-to-brittle transition in impact toughness at temperatures lower than 233 K. For the solution-treated condition, a minimum ductility is observed around 923 K. Transgranular cleavage cracking is the predominant fracture mode for solution-treated specimens tensile-tested at 77 K. The cleavage facets are identified as the {111} planes. This alloy shows considerable age-hardening capability. Aging at 823 K for 16 h results in an increase in yield stress of about 90% for temperatures ranging from 298 to 773 K, but causes brittle fracture at lower temperatures.

Growth kinetics of sintered NiO/ZrO2 (5 mol.% Y2O3) composites

Abstract This work uses X-ray diffraction and scanning electron microscopy to investigate the solution of NiO in ZrO 2 (with 5 mol% Y 2 O 3 , mainly in a metastable t′ phase as plasma sprayed powders) and the resultant growth kinetics of the NiO/ZrO 2 composite at 1600 °C. The tt-ZrO 2 transforms into cubic (c-) ZrO 2 within 1 h upon firing, and room temperature X-ray lattice parameter results indicate that the solubility of NiO in c-ZrO 2 is about 3 mol%. Within the solubility limit, both sintering and growth of c-ZrO 2 grains were enhanced by NiO addition. A further increase in the NiO content results in the formation of NiO particles which hinder the grain growth of c-ZrO 2 . For specimens with 10 mol% NiO the c-ZrO 2 grains were found to follow the t 1 3 growth kinetics, i.e. bulk diffusion controlled, while the intergranular and intragranular NiO particles coarsen according to t 1 4 and t 1 5 laws respectively. The interfacial energy of NiO/c-ZrO 2 is about 0.48 ± 0.1 J m 2 , inferred from the geometry of the NiO particles at the grain boundary.

Microstructure of zirconia-(MnZn ferrite) composites

Abstract This work uses scanning electron microscopy and transmission electron microscopy to study the microstructures of sintered ZrO 2 -(MnZn ferrite) composites with 0–20 wt.% ZrO 2 . The solid solubility of ZrO 2 in ferrite is very small according to lattice parameter variation determined by X-ray diffraction. The grain growth of MnZn ferrite is suppressed by the intergranular ZrO 2 particles for specimens with more than 5 wt.% ZrO 2 . For specimens with less than 5 wt.% ZrO 2 , the ZrO 2 particles are mainly intragranular and significantly faceted. Although there is no orientation relationship between the ZrO 2 partivles and ferrite matrix, the facets are determined to be {111} planes of ferrite. These {111} planes make up an octahedron which dictates the shape of the intragranular ZrO 2 particles. It is found that ZrO 2 particles less than 2.5 μm in size retain the tetragonal symmetry but those with larger size transform into monoclinic ZrO 2 .

Microstructures of first-stage aluminized coatings on nickel-based superalloys

Abstract Microstructures of first-stage aluminized coatings on Rene 80, MAR-M 247 and Inconel 713LC nickel-based superalloys are studied. The σ-Ni 2 Al 3 phase constitutes the major part of the coatings but a Ni 3 Al(γ′ phase) layer and a β phase layer exist at the substrate-coating interface. There is no preferred orientation relationship between the γ′ and β phases. The grain size decreases abruptly from 20–30 μm to less than 0.3 μm across the substrate-coating interface. Very fine and dense precipitates elongated in shape are present in the coating near the coating-substrate interface whereas precipitates more distant from the interface are larger and more spherical but less dense. An M 23 C 6 -type precipitate is commonly found in the coatings and its crystallographic orientation relationship to the δ phase is determined.

Effects of grain boundary carbide on the stress-strain curves of type 316 stainless steel

Abstract The presence of dense grain boundary carbide can result in a decrease in the uniform elongation and an increase in the tensile strength and strain hardening rate of type 316 stainless steel at room temperature. The stress-strain curves are analyzed using the Ludwigson equation σ = k 1 ϵ n 1 + exp ( k 2 + n 2 ϵ ). It is found than n 2 and n 2 decrease, k 1 increases slightly while k 2 is not affected by the presence of grain boundary carbide. The strain at which the Ludwigson equation reduces to the Ludwik equation (i.e. σ = k 1 ϵ n 1 ) decreases with increasing grain size and by the presence of grain boundary carbide. The significance of the results are discussed.

Reverse martensitic transformation in yttria-partially stabilized zirconia with TiO2 addition

Abstract Reverse martensitic transformations of monoclinic to tetragonal ZrO 2 in yttria-partially stabilized zirconia with various amounts of TiO 2 solution were studied by a grinding test. The relative amount of m-ZrO 2 was estimated by X-ray diffraction. The results indicate that TiO 2 decreases the tetragonal-to-monoclinic ZrO 2 martensitic transformation temperature but increases the reverse martensitic transformation temperature.

Morphology of tetragonal ZrO2 in TiO partially stabilized ZrO2

Etude au microscope electronique en transmission de la morphologie de disques de TiO-PSZ frittes sous vide

Defect microstructure in aluminized coatings

Abstract The defect microstructure in aluminized coatings of Rene 80, Inconel 713LC and MAR-M 247 was studied by transmission electron microscopy. Dislocations and subgrain boundaries were found within the s phase and interface dislocations between the s phase and the precipitates. The growth of s grains was inhibited by the polygonized σ lamellae and carbides in the diffusion zone and by α-Cr in the outer zone. Dislocation loops were found in the s phase throughout the coatings. The origins of the defects are also discussed.

The effects of grain boundary carbide on the low temperature tensile properties of type 316 stainless steel

Abstract The effects of grain boundary M23C6 precipitates on the low temperature (−196°C) tensile properties are systematically studied. For specimens aged at 650°C for 240 h and at 750°C for 100 h, the low temperature tensile strength, elongation and reduction in area are reduced severely and the specimens fail by brittle intergranular fracture. This is probably due to the dense grain boundary carbide and also to the grain boundary martensite in the chromium-depleted zone. The amounts of reduction in tensile strength, elongation and reduction of area increase with increasing grain size for specimens aged at 650°C for 240 h. The fracture strength is proportional to the inverse of the square root of grain size, and a critical stress intensity factor is determined.