Microstructure and mechanical properties of spherical zirconia-yttria granules

The methods used to prepare three spray dried yttria-zirconia powders have been shown to have a large effect on their behaviour during subsequent heat treatment and also on their resultant properties. Changes of morphology of the granules, their surface area, pore size distribution, porosity and compressive strength which occur during heat treatment have been determined. A concept of local densification was used to explain the observed changes in pore size distribution, where it was shown that distributions with pores smaller than 60–80 nm resulted in significant pore enlargement during the early stages of sintering. A theory based on fracture mechanics explained the changes in compressive strength of the granules.     

Flow properties of spray dried alumina granules using powder flow analysis technique

Commercially available alumina powders having an average particle size of <1 μm were spray dried to granules from aqueous slurries of different solid loadings. Spray drying is a one step granulation technique for obtaining the free flowing granules with desired sizes and morphologies from slurries. These free flowing spray dried granules on subsequent compaction processing results in the powder compacts with high densities and strength. The spray dried granules were evaluated for their flow properties in terms of cohesion index, compaction coefficient, powder flow speed dependency and caking properties using a powder flow analyzer attached to a texture analyzer. Spray-dried granules exhibited the cohesive index value of ～6.5 compared to a value of 16 for the commercially available powder. It is observed that a good correlation can be elucidated with respect to the powder particle size, surface area and morphology. The cake height ratio and compaction coefficient also complimented the above results. Powder flow analysis is an effective method to correlate the flow properties of the ceramic powders with the morphology, granule size and their distribution.     

Microstructure and mechanical properties of spray deposited and extruded 7000 series aluminium alloys

Abstract

The microstructure and mechanical properties of spray deposited 7000 series aluminium alloys were investigated. The 7000 type alloys were produced by the spray atomisation deposition method. These alloys were hot extruded and subsequently heat treated in the T6 and T7 temper conditions. Microstructural characterisation of the alloys was carried out by transmission electron microscopy (TEM). TEM studies revealed the presence of η′ and η(MgZn₂) hardening precipitates in both temper conditions. The mechanical properties were assessed through tensile and notched tensile tests using an Instron machine. It was observed that the 0.2% proof stress of these alloys after T7 temper decreased with increased elongation to fracture values.     

Microstructure and mechanical properties of spray formed 7055 aluminum alloy by underwater friction stir welding

Ultra-high strength spray formed 7055 aluminum alloy in which Zn is supersaturated solid solution requires strict control of heat input in welding process. In this paper, underwater friction stir welding is carried out in order to reduce heat input comparing with traditional friction stir welding and further improve the joint performances by varying welding temperature history. Through comparing the thermal cycle curves and distribution of residual stress of the plate welded in different media, the reason why the joint welded underwater shows a better performance is figured out. The result shows that tensile strength, hardness and plasticity of underwater welded joint are better than that welded in air. The underwater joint has a fine grained microstructure without “S line” defect, a typically distinct boundary between the weld nugget zone and the thermal mechanically affected zone and a narrow heat affected zone. The main strengthening phase in underwater joint is MgZn₂ .     

喷射成形CPM9V高速钢组织性能研究

为了提高CPM9V高速钢组织均匀性,采用喷射成形方法制备CPM9V高速钢,研究了喷射成形CPM9V高速钢热处理前后的微观组织.结果表明:喷射成形制备的CPM9V高速钢沉积坯晶粒细小,组织致密,无宏观偏析,沉积坯平均体密度为7.306 g/cm3,达到理论密度的98.1%;CPM9V高速钢沉积坯经热处理后组织为回火马氏体、铁素体和碳化物,二次回火硬度为52HRC,与粉末冶金CPM9V高速钢相当;组织中绝大部分为小于15μm的等轴晶,分布在晶界的碳化物主要为MC型碳化钒,分布在晶内的碳化物为VC和Mo的复合碳化物.     

Control of microstructure and disintegration properties of silica granules from PVA slurries by spray drying

The microstructure of spray-dried model granules, comprising silica microspheres and poly (vinylalcohol), was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with an ultramicrotome technique. Disintegration of granules was characterized by a shear method for granular beds, and by a compression test for single granules. The internal structure changed significantly with the pH of the slurry from which the granules were spray-dried. Granules from pH 7 slurry showed the smallest apparent density, and were disintegrated under the smallest applied load. By analysing the relationship between microstructure, apparent density and flow behaviour of the slurries, it was possible to obtain a guideline for preparation of appropriate granules with controlled microstructure and strength.     

Microstructure,mechanical and tribological properties of high velocity oxy fuel thermal spray coating: A review

Iron alloy based amorphous coating materials have enormous potential in wide range of applications such as petrochemical, aerospace, ocean, and electronic communications due to their better mechanical properties, chemical properties, magnetic properties and tribological properties. The industrial applications of coating are increasing rapidly due to many advancements in the material development and coating deposition techniques. The present paper reviewed the recent progresses in deposition technologies, development of new high order alloys and composite based coating materials. In this regard, change in microstructure, elemental composition, mechanical and tribological properties on performance of iron alloy based coating properties were presented. It can be concluded that the tribological properties of coating is dependent on pre-coating and post-coating factors. Pre-coating factors include coating deposition techniques, coating layer thickness and coating parameters such as spray distance, oxygen flow rate etc. Post-coating factors include microstructure, hardness, fracture toughness and adhesion strength. Therefore, multi-criteria decision making techniques can be the best approach to find the optimum formulation of coating materials to achieve desired set of objectives under the conflicting criteria.     

Microstructure and mechanical properties of horns derived from three domestic bovines

The microstructure and mechanical properties of horns derived from three domestic bovines (buffalo, cattle and sheep) were examined. The effects of water content, sampling position and orientation of three bovid horns on mechanical properties were systematically investigated by uniaxial tension and micron indentation tests. Meanwhile, the material composition and metal element contents were determined by Raman spectroscopy and elemental analysis respectively, and the microstructures of the horns were measured by scanning electron microscopy (SEM). Results show that the mechanical properties of horns have negative correlation with water contents and depend on sampling position and orientation. The spatial variations of the mechanical properties in horns are attributed to the different keratinization degrees in the proximal, middle and distal parts. And the mechanical properties of horns in the longitudinal direction are better than those in transverse. Among the three kinds of horns, the mechanical properties of buffalo horn are the best, followed by cattle horn, and those in sheep horn are the worst. This is due to the differences in material composition, metal element, and the microstructures of the horns. But the mechanical properties of buffalo horns are not dependent on the source of the buffalo. Therefore, regular engineered buffalo keratinous materials with standard mechanical properties can be obtained from different buffalo horns by using proper preparation methods.     

Microstructure and mechanical properties of sintered glass

Glass microspheres have been sintered under argon in order to obtain sintered brittle bodies over a large range of density. During sintering, the microstructure evolves from a stacking of spheres to a body containing isolated pores. This evolution of the microstructure is described using image analysis and mathematical morphology. Mechanical properties are also investigated as a function of density. Special attention was paid to fracture toughness because, due to the isotropic behaviour of glass, internal stresses of the second order do not exist. A maximum ofG _IC is observed and it can be correlated with changes in the morphological parameters.     

Microstructure and mechanical properties of macrodefect-free cements

The mechanical properties of macro-defect-free cements were investigated with the help of fracture mechanics and rheology; transmission electronic microscopy (TEM) and scanning electronic microscopy (SEM) were used to characterize the microstructure. The microstructure was found to consist of nanosized hydration products embedded in a cross-linked polymer matrix. The nanoscale composite structure of the cement is thought to play an important part in the mechanical properties.     

Microstructure and mechanical properties of Mg-HAP composites

In the present study, it has been attempted to develop biodegradable Mg-HAP (magnesium-hydroxyapatite) composite materials for bone replacement. At first the HAP powders were prepared by chemical synthesis process and synthesized powders were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Synthesized powders contain HAP as a major phase with tricalcium phosphate (β-TCP) as a minor phase. The Mg-HAP composites were prepared by adding different amounts of HAP powders to Mg melts and finally the billets were extruded. The microstructure of Mg-HAP composite was examined by optical microscope (OM). The presence of HAP in Mg matrix results in decrease of grain size of Mg-HAP composites. The theoretical and experimental hardness of the composites are compared with the addition of HAP. The tensile strength of composites is found to decrease with the addition of HAP, whereas compressive strength increases with HAP.     

Microstructure and mechanical properties of fluorcanasite glass-ceramics for biomedical applications

Four fluorcanasite glass-ceramics were fabricated by controlled heat-treatment of as-cast Glasses A–D. These compositions have been reported previously but essentially, Glass A had the stoichiometric composition (Ca₅Na₄K₂Si₁₂O₃₀F₄) and Glasses B–D were modified by reducing the Na₂O concentration (B), adding excess CaO (C) and P₂O₅ (D). The latter two compositions have been shown to have promising bioactive response in cell culture and simulated body fluid experiments. Devitrification of the stoichiometric composition resulted in poor mechanical properties with crumbling often observed on machining. As a result, no mechanical data could be obtained. In all modified compositions, heat-treatment between 780 °C and 900 °C resulted in measurable indentation fracture toughness (IFT) and biaxial flexural strength (BFS). IFT was optimised in Glass C at 800 °C (2.53 ± 0.02 MPa m^½), but the biaxial flexural strength (BFS) was low, 167 ± 17 MPa, compared to other compositions. For heat- treated Glass D optimum mechanical properties were obtained at 800 °C with BFS and IFT, 249 ± 23 MPa and 1.95 ± 0.01 MPa m^½, respectively. The relationship between the mechanical properties and microstructure is discussed.     

Microstructure and mechanical properties of hot-pressed SiC-TiC composites

Hot-pressed SiC-TiC composite ceramics with 0–100 wt% TiC have been investigated to determine the effect of composition (amount of TiC) on the elastic modulus, hardness, flexural strength and fracture toughness,K _IC. The composites exhibited superior mechanical properties compared to monolithic SiC and TiC, especially in fracture toughness,K _IC, value for 30–50 wt% TiC composite. The maximum values ofK _IC and room-temperature flexural strength were 6 MPa m^1/2 for a 50 wt % TiC and 750 MPa for a 30 wt% TiC composite, respectively. The observed toughening could be attributed to the deflection of cracks due to dispersion of the different particles. Although no third phases were detected by both TEM and XRD studies, an EDAX study and resistivity measurements indicated some possibility of solid solutions being present. The composites containing more than 30 wt% TiC, exhibited resistivity lower than 10^–3 cm which is favourable for electro-discharge machining of ceramics.     

Microstructure and mechanical properties of pitch-based carbon fibres

The microstructure of a series of mesophase pitch-based carbon fibres have been examined using X-ray diffraction, electron microscopy and Raman spectroscopy. It has been shown that the mechanical properties of the fibres are related directly to the response of this microstructure to deformation and, in particular, that the Young's modulus and tensile strength of the fibres are controlled directly by the fibre microstructure. It has also been shown that Raman spectroscopy can be a useful technique for not only characterizing the microstructure of the fibres but also for following molecular deformation in the fibres. It was found that the position of the 1580 cm^–1 Raman band for the fibres shifted with the application of stress and that the rate of shift per unit strain was proportional to the Young's modulus of the fibres. It was also shown that this reflected the higher degree of stressing of the graphite plane in the higher modulus fibres, consistent with recently developed theories which attempt to explain the dependence of the mechanical properties of carbon fibres upon the degree of orientation of the graphite planes.     

Microstructure and mechanical properties of orientated thermoplastic starches

Effect of orientation on microstructure and mechanical properties of thermoplastic starches with different amylose/amylopectin ratios was studied to understand the relationship between structure and properties in starch-based materials. Hydrogen bonds and the highly branched microstructure in amylopectin resist the orientation of the polymer chains. The unique microstructures of amylopectin form gel-balls and super-globes after gelatinization. A gel-ball contains mainly the chains from same sub-main chain in amylopectin, and remains in regular pattern and keeps a certain memory. The gel-balls and super-globes can be deformed under shear stress. However, the deformation does not alter the orientation ofthe polymer chains inside the gel-balls significantly. Orientation increases both modulus and yield stress but decreases the elongation, which is mainly contributed to by the orientation of amorphous phase. The oriented super-globe has large interior stress after retrogradation (crystallization) that results in micro-cracks and poor mechanical properties.     

Microstructure and mechanical properties of FexCoCrNiMn high-entropy alloys

The microstructure and tensile properties of Fe_xCoCrNiMn high-entropy alloys (HEAs) were investigated. It was found that the Fe_xCoCrNiMn HEA has a single face-centered cubic (fcc) structure in a wide range of Fe content. Further increasing the Fe content endowed the Fe_xCoCrNiMn alloys with an fcc/body-centered cubic (bcc) dual-phase structure. The yield strength of the Fe_xCoCrNiMn HEAs slightly decreased with the increase of Fe content. An excellent combination of strength and ductility was achieved in the Fe_xCoCrNiMn HEA with higher Fe content, which can be attributed to the outstanding deformation coordination capability of the fcc/bcc dual phase structure.     

Microstructure and mechanical properties of multi-constituent superlattice coatings

Superlattice nitride coatings with four different layer constituents, i.e., ZrN, MoN, NbN and AlN, were synthesized using an unbalanced closed-field magnetron sputtering coater. At small superlattice modulation periods, both MoN and AlN layers adapted to the cubic B1 structure due to a template effect, and the coatings exhibited a strong (2 0 0) preferred orientation. Increasing the modulation period above a critical value led to the formation of hexagonal MoN and AlN layers with diminishing (2 0 0) preferred orientation. These microstructure changes were reflected in the coating mechanical properties. Relatively high hardness and Young's modulus values were obtained at small modulation periods, which decreased dramatically above the critical modulation period. The effects of substrate bias on the layer crystallographic structure, coating preferred orientation and mechanical properties were similar to those of the modulation period.     

Microstructure and mechanical properties of accelerated sprayed concrete

Considering the different hydration processes of concrete without accelerator, sprayed concrete with low-alkali accelerator not only presents short setting times and high early-age mechanical properties but also yields different hydration products. This study presents an analysis of the mechanical properties of concrete with and without accelerator and sprayed concrete with three water–binder (w/b) ratios and four dosages of fly ash (FA) after different curing ages. It also examines the setting time, mineral composition, thermogravimetric–differential scanning calorimetry curves and microscopic images of cement pastes with different accelerator amounts. Furthermore, the setting time and microstructure of accelerated sprayed concrete with different w/b ratios and FA contents are examined. Results show that the retarded action of gypsum disappears in the accelerated cement–accelerator–water system. C₃A is quickly hydrated to form calcium aluminate hydrate (CAH) crystals, and a mesh structure is formed by ettringite, albite and CAH. A large amount of hydration heat improves the hydration rate of the cement clinker mineral and the resulting density, thereby improving mechanical properties at early curing ages. The setting times of the pastes increase with increasing w/b ratio and FA dosage. Thus, the hydration level, microstructure and morphology of the hydration products also change. Models of mechanical properties as functions of w/b, FA and curing age, as well as the relationship between compressive strength and splitting tensile strength, are established.     

Microstructure and mechanical properties of Ti-based solid-solution cermets

The microstructure and mechanical properties of various (Ti_1−xW_x)C-20 wt.%Ni cermets were investigated, where x varies from 0.07 to 0.3. Homogeneous solid-solution (Ti_1−xW_x)C powders were prepared by carbothermal reduction via planetary milling of Ti, TiO₂, WO₃ and carbon powder mixtures. The cermets made of the powders showed a simple core-rim structure consisting of solid-solution carbides. The hardness of the solid-solution cermets is somewhat lower than that of conventional cermets, but they show greater toughness. The transverse rupture strength increases with increasing W content.     

Influence of calcination temperature on the properties of spray dried alumina-zirconia composite powders

Alumina-zirconia composite powders containing 10, 12.5, 15 or 20 wt% zirconia were prepared by spray-drying the hydroxide gels. These powders were calcined at 650 and 950 °C. The spray-dried as well as the calcined powders were characterized by means of Coulter counter, Sorptometer, infrared spectroscopy (i.r.), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Initially the spray-dried powders are amorphous and spherical in shape with a diameter of 6 m and crystallize after calcination treatment at 950 °C. Sintered density of the 950 °C calcined powder compacts was higher than 650 °C calcined powder compacts. Compacts made from 650 °C treated powders retained 100% tetragonal phase after sintering irrespective of composition. Some amount of tetragonal phase is transformed into monoclinic phase in the composites containing higher amount of zirconia in the sintered compacts made from 950 °C calcined powders.