Effects of aluminum additions on the microstructure and mechanical properties of alumina-forming austenitic stainless steels

The mechanical properties, including tensile and impact properties at different testing temperatures of alumina-forming austenitic steels (25 % nickel, 20 % chromium) with different aluminum contents (0, 2.5 %, 5 % and 8 %) were investigated. Scanning and transmission electron microscopy together with tensile and impact properties tests were conducted. The results showed that the tensile strength of steels at 298 K increased obviously along with aluminum contents increasing, while plasticity decreased at the same, which attributed to the higher volume fraction and number density of spherical NiAl precipitation together with main ferrite in matrix. In addition, spherical NiAl particles dispersed easily in ferrite. In particular, the ultimate tensile strength of the sample with 8 % aluminum could reach 1398 MPa, with the elongation of 14 % at 298 K. However, NiAl precipitations would lose strengthening effects at high temperatures, but the plasticity could be improved. In addition, the sample with 5 % aluminum showed better comprehensive properties by comparison to other samples, and the ultimate tensile strength was 1018 MPa and 491 MPa at 298 K and 973 K with the elongation of 26 % and 43 %, respectively, enabling it to be promising material for industrial application in advanced nuclear systems.     

Mechanical characterisation of heat resistant power plant materials by creep and fatigue testing in controlled gas atmospheres

The continuing increase of steam parameters of fossil fuelled high efficiency power plants and new combustion concepts for the capture and storage of carbon dioxide lead to harsher service conditions for the components and structural materials of such facilities. The present work introduces a test concept that allows testing of candidate materials under simultaneous mechanical and corrosive loading. The material's reaction can be directly investigated under simulated temperature, load and corrosion conditions of modern installations. First results obtained for different heat resistant steels suggest a strong influence of the environmental medium on the fatigue and creep behaviour. Such findings complement the data that is available from the classical qualification process of the materials and may support the material selection for new power plant installations.     

Structure and mechanical properties of ZnAl40Cu3 alloy modified with rare earth elements

The influence of modification of rare earth elements on the structure and mechanical properties of ZnAl40Cu3 alloy is presented in this paper. The ZnAl40Cu3, ZnAl40Cu3SiM and ZnAl40Cu3Si (modified alloy) alloys were tested. The ZnAl40Cu3Si and ZnAl40Cu3 alloys were characterized and revealed a heterogeneous, fine‐grained, dendritic structure. The structure of the alloy ZnAl40Cu3SiM was much more homogeneous. It was found that the addition of silicon reduces the tensile strength. Addition of rare earth elements (REE) to the alloy with silicon resulted in the re‐growth of strength. It was also found that the modification of rare earth elements increases the hardness of the alloy.     

Enhancement of work‐hardening behavior of dual phase steel by heat treatment

The work‐hardening response and mechanical properties of dual phase steels originated from different initial microstructures under low and high martensite volume fractions were investigated using a typical carbon‐manganese steel. The modified Crussard‐Jaoul analysis was used for studying the work‐hardening stages and the deformation behavior of ferrite and martensite. It was revealed that the initial martensitic microstructure before intercritical annealing is much better than the full annealed banded ferritic‐pearlitic and spheroidized microstructures in terms of work‐hardening capacity and strength‐ductility trade off. By increasing the amount of martensite, via intercritical annealing at higher temperatures, the ductility decreased but the tensile toughness of dual phase steels increased toward reaching the domain of extra‐advanced high‐strength steels due to the enhancement of work‐hardening rate.     

Correlation of injection moulding parameters with mechanical and morphological aspects of natural fibre reinforced thermoplastics

The mechanical behaviour of fibre reinforced composites depends – amongst other things – on the morphological structure. This in turn is greatly affected by the processing conditions. In this study a 10 weight % flax fibre reinforced high density polyethylene composite is prepared by extrusion compounding followed by injection moulding. The effect of injection temperature, speed and rotational screw speed on the morphology of fibres and matrix are studied and related to the tensile and impact behaviour of the composites. Results indicate that fibre length is easily affected by all parameters under consideration. Whereas a higher injection temperature allows the preservation of fibre length, an excessive increase in temperature, however, leads to their thermal degradation. Increased injection and rotational speeds further introduce excessive shear stresses on the fibre, causing their breakage, similarly leading to reduced mechanical performance. Matrix structure is mainly affected by the injection temperature, where its increase leads to the reduction in the degree of crystallinity and thus also a decrease in tensile strength. Other processing parameters prove to have minor effect on matrix morphology.     

Enhanced surface properties and contact fatigue performance of Cr4Mo4V bearing steel subjected to ultrasonic surface rolling processing

The paper presents the experimental studies on the enhanced comprehensive properties of Cr4Mo4V bearing steel using ultrasonic surface rolling process. Considerable improvements in mechanical properties and rolling contact fatigue performance are achieved in the present study, accompanied by the characterization of surface microstructures. The ultrasonic surface rolling process promotes the formation of fine nanocrystalline structures and nano-sized elongated grains with severe deformation, leading to the increasing residual stress, micro-hardness and high temperatures hardness. The crack propagation and delamination pit in the surface after ultrasonic surface rolling process is inhibited, further enhancing the rolling contact fatigue life of Cr4Mo4V bearing steel.     

Experimental investigation on mechanical properties and wear characterization of Al-Si12CulMg1 aluminium alloy reinforced with titanium diboride and boron carbide particulate hybrid composites using stir casting process

LM13 aluminium alloy (Al−Si12CulMg1) with titanium diboride (TiB₂) and boron carbide (B₄C) particulate hybrid composites have been prepared using stir casting process. Wt% of titanium diboride is varied from 0–10 and constant 5 wt% boron carbide particles have been used to reinforce LM13 aluminium alloy. Microstructure of the composites has been investigated and mechanical properties viz., hardness, the tensile strength of composites have been analyzed. Wear behavior of samples has been tested using a pin on disc apparatus under varying load (20 N–50 N) for a sliding distance of 2000 m. Fracture and wear on the surface of samples have been investigated. Microstructures of composites show uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt % of reinforcements. Dry sliding wear test results reveal that weight loss of composites increased with increasing load and sliding distance. Fracture on the surface of composites reveals that the initiation of crack is at the interface of the matrix and reinforcement whereas dimples are observed for LM13 aluminium alloy. Worn surface of composites shows fine grooves and delamination is observed for the matrix.     

Numerical investigations on the mechanical properties of metallic hollow spheres structure with perforations under compression

This paper numerically investigates the compressive mechanical properties of the perforated hollow spheres structures with different geometrical and physical properties. In these structures, the metallic hollow spheres are perforated regularly with several holes, which open the inner sphere volume and surface and are bonded in simple cubic, body-centered cubic and face-centred cubic patterns. The 5×5 cells finite element models under uniaxial compression are established by ABAQUS 6.14 software for simulation. The influence of the spheres’ spatial pattern, as well as base materials for the spheres and bonding necks on the structural mechanical properties are evaluated. By changing the wall thickness, hole diameter and bonding radius in the body-centered cubic packing finite element model, the elastic modulus, Poisson's ratio and initial yield stress are calculated and discussed as functions of these geometrical parameters and their average densities.     

Thermisch‐mechanisches Ermüdungsverhalten der partikelverstärkten Aluminiumknetlegierung EN AW‐6061‐T6 und die Entwicklung von Eigenspannungen im Matrixwerkstoff unter thermisch‐mechanischer Beanspruchung

Thermal mechanical fatigue behaviour of particle reinforced EN AW‐6061‐T6 and development of residual stresses in the matrix material by thermal mechanical loading The behaviour of non reinforced and 15 Vol.‐% α‐alumina particle reinforced wrought aluminium alloy EN AW‐6061‐T6 in thermal mechanical fatigue loading was investigated at different maximum temperatures. The tests were performed in strain controlled mode by means of an electro‐mechanical testing machine. Alternating load deformation and life cycle behaviour either materials were compared. It came out, that the reinforcement leads to an decreasing thermal mechanical fatigue life cycle while keeping constant the maximum temperature and mechanical loading. The two materials showed softening behaviour due to high maximum temperatures of 573 K to 673 K. However, there is an intense scatter of the number of cycles to failure of the non reinforced alloy aggravating the interpretation of the results. On the other hand the thermal mechanical life cycle increases in combination with increasing maximum temperatures. Simultaneously the part of plastic deformation in mechanical loading increases for both materials, while for a constant total strain range the effective maximum and minimum stresses are decreasing. Furthermore, the development of residual stresses in the matrix of the reinforced alloy by thermal mechanical fatigue loading was analysed. It was observed that only small absolute values of residual stresses will be obtained for these loads. Nevertheless, tendencies of mounting tensile residual stresses can be identified in the direction of thermal mechanical fatigue loading and subsequently reduction of the residual stresses.