Effect of iron on the setting properties of α-TCP bone cements

New ceramic materials with the ability to set like cement, after mixing a powder phase made of one and/or several of these new reactants and a liquid phase, have been obtained within the ternary system “CaO-P₂O₅-FeO”. These new reactants have magnetic properties, i.e. cement made from them maintains its magnetic property during the whole setting and hardening. These new materials can be of use, for example, in dental applications, in the treatment of certain types of bone cancer and, in general, in the fields of Biomaterials and Bone Tissue Engineering. In this article, we report on the effect of iron-modified α -tricalcium phosphate, which is the main reactant of commercial calcium phosphate bone cements, on their new setting and hardening properties.     

Determination of diffusion coefficient of oxygen in α-iron from internal oxidation measurements in Fe-Si alloys

The diffusion coefficient of oxygen in -iron was determined by internal oxidation measurements on iron alloys with various contents of silicon in a temperature range from 1073 to 11 73 K with particular attention to the effect of oxide particles in the oxidation layer. The oxide in the oxidation layer and the concentration of silicon present as an oxide, as well as the rate constant for penetration of the oxidation front were determined. The diffusion coefficient of oxygen in the layer, D _O ¹⁰ , calculated using the rate equation for internal oxidation, increases with the increase in volume fraction of the oxide, f ¹⁰. This result indicates that the existence of oxide particles accelerates oxygen diffusion. Therefore, the diffusion coefficient of oxygen in -iron is determined by extrapolating D _O ¹⁰ to f ¹⁰ = 0, giving good agreement with results obtained in our recent investigations.     

Effect of alloying elements on hydrogen diffusivity in α-iron

The effect of Cr, Ni, Mo, Si and Cu on the diffusivity of hydrogen in-iron is studied in the temperature range of 160 to 430° C at a hydrogen pressure of 1 atm. The diffusivity of hydrogen was determined by absorption rate experiments using Sievert's type apparatus. The results show that the diffusivity of hydrogen in iron alloys decreases and the activation energy increases, as the concentration of the alloying elements increases, except Cu and Ni. The trapping parameters of hydrogen in iron alloys on the basis of Oriani's approach are calculated. The results show that Si, Mo and Cr are in order of increasing trap energy and that Cu and Ni have a negligible effect on hydrogen trapping. This can be explained by taking account of both chemical affinity effects and elastic strain effects of alloying elements on hydrogen trapping.     

Effect of additives on sintering of α-cristobalite

Sintering is performed for the pure α-cristobalite, with TiO₂ additive, and with CaO additive powder compacts. The sintering temperatures were 1500, 1515, and 1525 °C for different dwell times. The master sintering curve theory is applied to the densification data and the activation energies are obtained. The splitting strength is measured for the sintered specimens. It is found that CaO decreases the activation energy due to the formation of liquid phase at the used sintering temperatures. The TiO₂ increases the activation energy because it exists as solid particles at the used sintering temperatures. The measured splitting strengths of the sintered specimens are shown to be best expressed by a sigmoid function of the work of sintering.     

Effect of silicate incorporation on in vivo responses of α-tricalcium phosphate ceramics

In addition to calcium phosphate-based ceramics, glass-based materials have been utilized as bone substitutes, and silicate in these materials has been suggested to contribute to their ability to stimulate bone repair. In this study, a silicate-containing α-tricalcium phosphate (α-TCP) ceramic was prepared using a wet chemical process. Porous granules composed of silicate-containing α-TCP, for which the starting composition had a molar ratio of 0.05 for Si/(P + Si), and silicate-free α-TCP were prepared and evaluated in vivo. When implanted into bone defects that were created in rat femurs, α-TCP ceramics either with or without silicate were biodegraded, generating a hybrid tissue composed of residual ceramic granules and newly formed bone, which had a tissue architecture similar to physiological trabecular structures, and aided regeneration of the bone defects. Supplementation with silicate significantly promoted osteogenesis and delayed biodegradation of α-TCP. These results suggest that silicate-containing α-TCP is advantageous for initial skeletal fixation and wound regeneration in bone repair.     

Effect of additives on microstructure of Ca α-sialon

Three kinds of additives were added into Ca α-sialon, (Ca_0.6Si_10.2Al_1.8O_0.6N_15.4). It was found that the additives resulted in more of the liquid phase during sintering, which promoted the completion of the α→α′ transformation and the development of the elongated morphology characteristic of α-sialon grains. Comparison was made concerning the effect of the amount and type of additives on the microstructural development of Ca α-sialon. Phase and property analysis was also carried out on the hot-pressed samples.     

Effect of processing on toughness of Ca α-sialon ceramics

The influence of processing on microstructural development of Ca -sialon composition (Ca _x Si_12–3x Al_3x O _x N_16–x ) with x = 1.8 was studied by dwelling at different intermediate temperatures before reaching the final sintering temperature. The microstructural observation results have showed the different aspect ratios of elongated grains obtained by the various processing conditions, reflecting the effect of the number of nuclei of -sialon on morphology of grains during sintering. Improved toughness was achieved by applying low temperature dwelling for Ca -sialon compositions with low x values. The toughness showed an increase of 33% and 16% for x = 0.6 and 1.0 compositions respectively with middle dwelling processing at 1350°C for 3 h before reaching 1750°C for 1 h by hot-pressing.     

Effect of Al Content on Precipitation of α_2 Ordered Phase in Ti-Al-Sn-Zr-Mo-Si-Nd Alloys

The precipitation characteristics of the α2 ordered phase in Ti-AI-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the α2 ordered phase changed with temperature and Al content. The dislocations were the only places where the α2 ordered phase could precipitate at higher temperature near the critical transformation temperature for each alloy experimented. With the addition of Al content, the critical transformation temperature of α2 ordered phase increased. When the aging temperature was relatively low (650℃), the precedent precipitation of α2 ordered phase took place in primary a phase at the early stage of aging, in the duplex microstructure (the primary a with the transformed (3) of the alloys with lower Al content. But after certain aging time (50 h), the size of α2 particles was almost equal in both the primary a and the transformed β. And no obvious growth of α2 particles could be observed after 50 h.     

Effect of microstructure on oxygen permeation in SrCo0.8Fe0.2O3−δ

The effect of microstructure on oxygen permeation in SrCo0.8Fe0.2O3– membranes was investigated using disc samples fabricated under different processing conditions of applied pressure and sintering temperature. The average grain size of the samples was found to remain unchanged as a function of applied pressure, but increased considerably when the sintering temperature was increased from 950 to 1200°C. This change in grain size has a strong effect on the oxygen permeation flux, which increased considerably as the grain size was decreased. The density as well as the microhardness of these samples were also measured and found to change slightly as the processing conditions were changed.     

Studies on fusion zone fracture behaviour of electron beam welds of an α+β-titanium alloy

A study was undertaken to understand the fusion zone fracture behaviour of electron beam welded +-titanium alloy Ti-6.5 Al-3.3 Mo-1.8 Zr and 0.25 Si. The effect of base metal microstructure, the amount of heat input and post weld heat treatment cycle on the all-weld tensile properties and fracture behaviour was investigated in this work. In general, it was found that the tensile strength and ductility of +-base welds are higher than that of the -base welds and the difference was attributed to the presence of wider fusion zone grains of -base welds. The -base weld tensile specimens always exhibited an intergranular fracture mode irrespective of the amount of heat input. The single pass low heat input +-base welds failed by ductile transgranular fracture mode, while high heat input single pass welds failed by a mixed mode (intergranular plus faceted) fracture. In general high heat input welds showed low ductility mainly on account of the strain localization effects at the grain boundary alpha phase. Post-weld heat treatments of +-base welds resulted in the improvement of tensile ductility and were associated with transgranular fracture due to the absence of strain localization effects at the grain boundary alpha phase.     

Effect of austenitising temperature on tensile properties of Cu–Ni austempered ductile iron

Abstract

The effect of austenitising temperature on the microstructure, mechanical properties, and dimensional stability of a spheroidal graphite iron containing copper and nickel has been investigated. It was found that as the temperature increased the amount of carbon taken into solution by the austenite increased thus reducing the driving force of the original austenite to bainitic ferrite and high carbon austenite. As a consequence, the amount of retained austenite increased, but its stability decreased. This placed an upper limit on the austenitising temperature and on the amount of retained austenite permissible. All properties other than hardness showed maximum values after austenitising at 900°C. It was also found that increasing the solution treatment temperature increased the dimensional stability.

MST/1116     

Effect of hydrolysed aluminium treatment on rheological characteristics of α-alumina slurries

This paper describes the process for the hydrolysed aluminium treatment (HA) on alumina surface and its influence on the rheological characteristics of alumina slurries. Three different commercial grade aluminas were provided with the surface treatment with hydrolysed aluminium using aluminium nitrate and hexamethylenetetramine (HMTA) under controlled conditions. The HA treatment increased the concentration of Al-OH surface sites resulting in higher H⁺ adsorption on the alumina surface. A highly concentrated (>55 vol%) electrostatically stabilized alumina slurry was prepared from HA treated alumina powders. The rheology of such slurry was studied and the results on the viscosity and yield stress are presented. The alumina slurries followed the Casson Model flow behaviour. The wet and flow behaviour of the alumina with and without HA treatment was also studied and the results are compared. The surface treatment showed the advantage of maintaining low viscosity and yield stress of alumina slurries even at higher solids loading (>55 vol%) that are prepared in the acidic aqueous medium. The results on viscosity and yield stress were compared with that of the polyelectrolyte dispersed system.     

Effect of addition of tin on the microstructure and machinability of α-brass

This study was aimed at developing lead-free brass alloys with the goal of substituting lead element with tin. For this purpose, lead-free alloys with tin were developed and the microstructure, hardness and machining behaviour of the Cu–30%Zn alloy was compared with Cu–30%Zn–x%Sn (x?= 1.2, 3.2, 5.4, 8, 11.4, 13.9, 17.4). The results showed that the addition of Sn to single-α phase brass led to the formation of duplex (α?+?β′) brass and then the formation of (β′?+?? ) brass both with increased hardness. In addition, the addition of Sn to Cu–30%Zn alloy led to the decrement of equivalent machining forces (F_m), surface roughness and also the promotion of chip fragmentation due to the formation of the β′ phase, which is an improvement in machinability.     

Effect of Different Rare-Earth on Microstructure and Properties of α-Sialon Ceramics

Densified Yb-, Y-, Dy-, Sin- and Nd-α-Sialon ceramics were prepared by two-step hot sintering. The variation of microstructure and properties with different rare-earth was investigated. The ceramics doped with smaller cations （Yb3＋, y3＋ and Dy3＋） are fully composed of α-Sialon, while in the larger cations （Sm3＋ and Nd3＋） doped ceramics also exist a few intergranular phase Mt （Re2Si3-xAlxO3＋xN4-x） in triple-point pockets. With increasing the radius of the rare-earth cations, the elongated α-Sialon grains form instead of the equiaxed grains in Yb-α-Sialon, and the aspect ratio of grains increases. All the ceramics possess high hardness, and the value of 21 GPa is achieved for Yb- and Y-α-Sialon. With increasing the ionic size of rare-earth, the hardness decreases slightly but the toughness tends to increase. Nd-α-Sialon possesses the highest toughness with the value of 5.4 MPa·m^1/2.     

Effect of oxygen on short-range order in the Ba1−xBixF2+x solid solution

Various compositions within the range of the fluorite-type solid solution in the BaF₂–BiF₃–BiO_l.5 system are investigated by impedance spectroscopy. This study is carried out along two lines of compositions: δ₁, corresponding to the Ba_l−2z/3Bi_2z/3F_2+4z/3O_z solid solution, where z is the oxygen rate; and δ₂, corresponding to the Ba_l−xBi_xF_2+x−0.30O_0.15 solid solution, where x is the bismuth rate. An approach to the nature of the fluorine–oxygen order is proposed which derives from the clustering process in the Ba_l−xBi_xF_2+x fluoride solid solution.     

Effect of welding parameters on diffusion bonding of type 304 stainless steel–copper bimetal

Abstract

Stainless steel AISI type 304 and electrolytic cold rolled copper were joined by diffusion bonding at temperatures ranging from 650 to 950°C, for times from 5 to 45 min, and at pressures from 2 to 12 MPa. After bonding the microstructure of the interface was investigated, including the grain size, and shear and tensile strengths of the bonded specimens were determined. From the results, it was seen that the bond shear strength was dependent on interface grain boundary migration and on grain growth during the bonding process. In addition, attempts were made to find a relationship between grain size and shear strength in the bonding area. Taking into account the results of shear testing and microstructural observation, for a sound bond, optimum bonding conditions were obtained at temperatures of 800–850°C for 15–20 min at 4–6.5 MPa. The fracture behaviour of the diffusion bonded joint was investigated by means of shear and tensile testing under different bonding conditions. It was found that both shear and tensile strengths of the bonds were sensitive to the bonding conditions, and the intermetallic phases did not affect these parameters. Furthermore, the value of shear strength of the bond surface determined by shear testing was higher than the shear strength of the fracture surface determined by tensile testing.