Multiple heat isothermal stress rupture correlations for type 316L(N) stainless steel and their use Part 2 – Applications for nuclear grade type 316L(N) stainless steel base metal and its weld metal

Abstract

The 'reference' multiple heat isothermal stress rupture correlations for stainless steel types 316 and 316L(N) base metals derived in Part 1 are used for establishing those for a specific 316L(N) stainless steel base metal and also its weld, both candidates for the forthcoming prototype fast breeder reactor at Kalpakkam. The phases that form in the weld metal during creep are the same as those in the base metal; however, the uniformly distributed δ ferrite ( ~ 7 ferrite number) in vermicular morphology present in the initial microstructure accelerates their formation and increases their quantities, resulting in poorer stress rupture properties. A simple modification allows for correlating and extrapolating the weld data to long rupture lives using the multiple heat isothermal correlations developed for the base metal.     

High strength Al2O3p/6061 Al composites: effect of particles,subgrains and precipitates

Abstract

Composites of 6061 Al reinforced by Al₂O₃ particles have been produced by squeeze casting followed by hot extrusion and a T4 precipitation hardening treatment. The tensile properties at room temperature have been determined and analysed based on microstructural parameters. The strength contributions from the matrix, particles, subgrains and precipitates have been estimated individually, and then based on an assumption of linear additivity, the yield stress values of the composites under the extruded and heat treated conditions have been calculated. Good agreement between the calculated and experimental values has been found, illustrating the suitability of the process for the manufacture of strong composites, with a maximum yield stress of 524 MPa obtained for a composite containing 60 vol.-%Al₂O₃.     

Kinetic equations for non-equilibrium grain boundary segregation induced by applied tensile stress

Abstract

Based on an earlier model, a set of kinetic equations is derived to formulate the process of non-equilibrium grain boundary segregation induced by a low tensile stress. These kinetic equations allow excellent simulation of the grain boundary segregation of phosphorus and sulphur observed in steels subjected to low tensile stresses. The simulation results justify both the earlier model and the present kinetic equations. They also show that an applied tensile stress can increase the diffusion rate of solute-vacancy complexes and decrease that of isolated solute atoms significantly, and can also bring forward the critical time of non-equilibrium segregation for phosphorus and delay that for sulphur.     

Wear behaviour of in situ Cu–Al2O3 composites produced by internal oxidation of as cast alloys

Abstract

In the present study, the wear behaviour of Cu–Al₂O₃ composites and Cu–Al alloys has been investigated. The experiment involved casting of Cu–Al alloys with 0·37, 1, 2 and 3 wt-% of aluminium under inert gas atmosphere. The composites were produced by internal oxidation of alloys at 950°C for 10 h in presence of Fe₂O₃ and Al₂O₃ powders mixture. The microstructures of composites were studied using SEM and atomic force microscopy. To identify wear behaviour of specimens, dry sliding pin-on-disk wear tests were conducted according to ASTM G99-95a standard. The normal loads of 20, 30, and 40 N were applied on specimens during wear tests. The sliding speed and distances were selected as 0·5 m s^–1 and 500, 1000 and 1500 m respectively. To specify the wear mechanisms, the worn surfaces of composites were examined by SEM equipped with EDX. According to wear test results, increasing applied load and sliding distance leads to more volume loss in all specimens. Composites represent better wear resistance in comparison to alloys. Additionally, increasing the volume fraction of alumina particles in composites enhances the wear resistance, especially under high applied load. The wear mechanisms are mainly abrasion, oxidation and delamination.     

Preparation of tungsten base composite powder by electroless nickel plating

Abstract

Fine tungsten powder with an average size of 8 μm was coated by electroless nickel plating with hydrazine and sodium hypophosphite reducing agents to obtain Ni and Ni–P coatings, respectively. The influence of process parameters such as temperature, pH and time of electroless plating was investigated. As coated composite powders were characterised by energy dispersive spectrometer analysis and scanning electron microscopy. It was found that, high homogeneity Ni/Ni–P coatings are deposited around the tungsten particles. Also it was shown that deposited mass on the powders increases as the temperature and pH of bath increase, but with different deposition rates depending on coating type. Furthermore, other results indicate that at higher pH values, the P content in the Ni–P coating decreases, leading less impurity in the final composite powders.     

Direct reduced iron production using cold bonded carbon bearing pellets Part 1 – Laboratory metallisation

Abstract

A new cold bonding technology for producing coal bearing composite pellets was developed. Alumina cement was used as binder, which gave high mechanical strength to the pellet even at elevated temperatures. Laboratory test results showed that the metallisation rate of the pellets was high owing to the intimate contact of the particulates of coal and the iron ore in the pellet. The developed cold bonding method can also be used to recycle electric arc furnace (EAF) dust, from which valuable zinc and lead can also be recovered.     

Reaction rate and product morphology in carbon composite iron ore pellets with and without Portland cement

Abstract

The aim of this work is to study the reaction rate and the morphology of intermediate reaction products during iron ore reduction when iron ore and carbonaceous materials are agglomerated together with or without Portland cement. The reaction was performed at high temperatures, and used small size samples in order to minimise heat transfer constraints. Coke breeze and pure graphite were the carbonaceous materials employed. Portland cement was applied as a binder, and pellet diameters were in the range 5·6–6·5 mm. The experimental technique involved the measurement of the pellet weight loss, as well as the interruption of the reaction at different stages, in order to submit the partially reduced pellet to scanning electron microscopy. The experimental temperature was in the range 1423–1623 K, and the total reaction time varied from 240 to 1200 s. It was observed that above 1523 K the formation of liquid slag occurred inside the pellets, which partially dissolved iron oxides. The apparent activation energies obtained were 255 kJ mol^–1 for coke breeze containing pellets, and 230 kJ mol^–1 for those pellets containing graphite. It was possible to avoid heat transfer control of the reaction rate up to 1523 K by employing small composite pellets.     

Effect of γ-Radiation on the Mechanical Performance of Hybrid Rice Straw/Seaweed-Polypropylene Composites

Hybrid composites of rice straw (Rs)/seaweed (Sw) and polypropylene (PP) were prepared at a fixed filler ratio of 30:70 and variable ratio of the two reinforcements, viz. 30:0, 25:5, 20:10, 10:20, 0:30 by weight. Mechanical properties of the composites such as tensile strength (TS), bending strength (BS), impact strength (IS) and elongation at break (Eb%) were investigated and the composite formulation of 20:10:70 (Rs:Sw:PP) was found to be optimum that showed TS = 2.8 MPa, BS = 68 N/mm², IS = 2.5 kJ/mm² and Eb = 50%. For better compatibility, Rs and Sw were subjected to surface treatment using various intensities of γ-radiation to prepare improved hybrid composites. γ-irradiated filler hybrid composites significantly enhanced mechanical properties and the composite in which fillers were irradiated at 100 krad achieved maximum enhancement with TS = 35 MPa, BS = 75 N/mm², IS = 2.7 kJ/mm² and Eb = 68%. Water absorption capacity of the different composites was also studied and irradiated filler composites showed less water uptake.     

Shear bond strengths of five intraoral porcelain repair systems

In fixed prosthodontics, fracture of the porcelain veneer is not an uncommon problem under clinical conditions due to, e.g., malfunction, trauma or technical failures. To avoid time-consuming and cost-intensive renewal of the entire restoration, repair of the chipped veneer is desirable. The aim of this in vitro study was to evaluate the shear bond strengths of five intraoral porcelain repair kits based on different chemical bonding systems. 45 metal plates veneered with feldspathic porcelain were fabricated. The surface treatment was performed using five porcelain repair systems based on tribochemical silica coating (Cojet), mechanical roughening (Silistor, Cimara, Ceramic Repair) or etching (Clearfil Repair) followed by application of silane coupling agents (five specimens each). Cylinders of composite resin of Charisma and Pertac Hybrid were bonded using Cojet, Silistor, Cimara and Ceramic Repair, and of Clearfil AP-X with Clearfil Repair onto the porcelain specimens. After thermocycling (5000 cycles, 5–55°C) shear bond strength was measured according to ISO 10477 followed by assessment of the failure mode. Statistical analysis was carried out with one-way ANOVA and Bonferroni–Dunn's multiple comparisons post-hoc analysis for test groups (α = 0.05). Shear bond strengths higher than 10 MPa were found for all test groups except for Ceramic Repair with Pertac Hybrid (8.1 ±1.3 MPa), which was significantly lower than all other groups (P < 0.05). Highest shear bond strength was found for Silistor with Charisma (23.1 ± 5.8 MPa), which was significantly higher (P < 0.05) than all other groups except Cojet with Charisma (17.8 ± 3.6 MPa) and Clearfil Repair (20.3 ± 5.0 MPa). Cojet and Silistor with Charisma, Cimara, as well as with Clearfil mainly showed cohesive or mixed failure modes (cohesive and interfacial). Bond strengths of the combinations Silistor-Charisma, Clearfil Repair-Clearfil AP-X and Cojet-Charisma were superior to all other combinations used in the present tests.     

Avoidance of fabricational thermal residual stresses in co-cure bonded metal-composite hybrid structures

In this work, a smart cure cycle with cooling, polymerization and reheating was devised to nearly completely eliminate thermal residual stresses in the bonding layer of the co-cure bonded hybrid structure. In situ dielectrometry cure monitoring, DSC experiments and rheometric measurements were performed to investigate the physical state and the cure kinetics of the neat epoxy resin in the carbon fiber/epoxy composite materials. From the experimental results, an optimal cooling point in the cure cycle was obtained. Also, process parameters such as cooling rate, polymerization temperature and polymerization time in the curing process were investigated. Then, the thermal residual stresses were estimated by measuring the curvatures of co-cure bonded steel/composite strips and their effects on the static lap-shear strengths of co-cure bonded steel/composite lap joints were measured. Also, the effects of thermal residual stresses on the tensile strength, the interlaminar shear strength and the interlaminar fracture toughness of the composite material itself were measured using tensile, short beam shear and double cantilever beam tests. From these results, it was found that the smart cure cycle with cooling, polymerization and reheating eliminated the thermal residual stresses completely and improved the interfacial strength of the co-cure bonded hybrid structures, as well as the tensile strength of the composite structures.