Volume 54, Issue 6

HP alloy Fe-25Cr-35Ni is widely used in petrochemical industry, because of its good corrosion and oxidation resistance at high temperature. As-cast microstructure of HP alloy consists of eutectic carbide in discontinuous network. After service in carburizing atmosphere at high temperature, the microstructure of serviced HP alloy, which consisted of carbide network that was thicker and coarser than as-cast specimens as well as irregular shape carbide, lost its tensile strength and fracture elongation properties. However, the hardness increased. The serviced HP alloys were heat treated in 12 conditions, which could be classified in four main categories. The first one was solutionized at three different temperatures — 1,373, 1,423 and 1,473 K. The second was solutionized at 1,373 K and aged at 1,073, 1,173 and 1,273 K. The third was solutionized at 1,423 K and aged at 1,073, 1,173 and 1,273 K. The last one was solutionized at 1,473 K and aged at 1,073, 1,173 and 1,273 K. The process time for solution was 21.6 ks and aging is 86.4 ks for all conditions. The result showed that the amount of Cr rich carbide vastly decreased after heat treatment in all conditions. The Vicker hardness values (HV) of all heat treated specimen decreased comparing to that of serviced alloy. In conclusion, heat treatment provided new microstructures with lower amount of carbide networks of serviced alloy which resulted in improvement of tensile strength and fracture elongation properties.

Recently, the cost factor of raw materials has emerged continuous improvement of tin-copper solder alloys. This work aims to improve the microstructural and mechanical properties of the eutectic tin-copper solder alloys by addition of nickel, cobalt and indium. The temperature profile of reflow soldering in surface-mount assembly was simulated to produce realistic joint microstructures. Key properties for electronic soldering were characterized, i.e. melting behaviour, solidification beha-viour, wettability, electrical resistivity, microstructures and mechanical properties. The results showed that addition of Ni, Co and In can effectively improve the mechanical properties of Sn-0.7Cu solder alloy i.e. microhardness and shear strength by providing preferred interfacial morphology and formation of intermetallic compound precipitates. The new solder alloys also showed reduced liquidus and solidus temperatures whereas no significant degradation of other key properties were seen.

Recycling of ADC12 alloy scraps for fabrication of open-cell aluminium foams has been conducted via pressure infiltration method of replication process. The scrap, up to 50 wt.-%, was melted with pure aluminium billet, followed by infiltration in a replicated mold of polyethylene foam structure. Compared with the pure aluminium foam, the compressive strength and hardness are higher the foams with recycled scraps of. The improvement of mechanical properties is due to the presence of Si hard phase in Al matrix. The strength and hardness of the foams also increase with increasing content of scrap.

Residual stress analyses were performed on nitrided, low alloy steels by varying the measuring conditions. The measurements were carried out in the compound layer on ∊-Fe 2–3 N and γ′-Fe 4 N as well as in the diffusion layer on α-Fe. By considering different criteria, tensile residual stresses of up to 300 MPa produced, {111}-interference, for ∊-Fe 2–3 N using CuKα radiation on the specimen's surface. After removing 5 μm from the surface, compressive residual stresses occur in this phase. On employing the CrKα and CuKα radiation, relatively high compressive stresses are obtained of up to above −1000 MPa for γ′-Fe 4 N. For measurements using CrKα radiation, compressive residual stresses result in the diffusion layer for α-Fe, which have a maximum value below the surface. Here, the measurements of the {211}-interference give lower residual stress magnitudes than measurements of the {110}- and {200}-interferences. By verifying the phase superpositions, the linear distributions of line positions or the comparable loading stress analysis using XRD or strain gauges, the results determined at the {211}-interference appear to be realistic. Attention should be paid to the high penetration depth of CrKα radiation. Here, no gradients of the investigated stress states may exist which are too large. The steel possessing a higher content of nitride forming elements such as Al, for example, mainly exhibit the highest compressive residual stresses. In the diffusion layer of 34CrAlNi7-10, maximum compressive residual stresses of −800 MPa result at {211}-interference in α-Fe.

In this study, elastic-plastic fracture toughness of an aluminum alloy is investigated. J-integral was calculated using the finite element software and formulation. Crack tip opening displacement (CTOD) is determined by using the plastic hinge model (δ ph ) and direct measurement (δ 5 ). J-Δ a and CTOD-Δ a resistance curves are constructed and compared with those obtained from formulation and those generated from test data, respectively. Good agreement has been obtained between the test results, the formulation and the results of the finite element analysis. The relationship between δ ph and δ 5 is nonlinear and as CTOD increases δ 5 becomes larger than δ ph . The relationship between J-integral and CTOD is found to be linear for both δ ph and δ 5 . It has been seen that the proportionality constant d n considerably depends on the method of calculation of CTOD.

Vibration based on structural damage detection (DD) is an important subject in many fields of engineering. Detection of possible damage locations before destructive stiffness losses in the engineering structures occur, is a main goal of DD. This paper describes the damage detection in structural elements by means of Particle Swarm Optimization algorithm (PSO). In this regard, the finite element model of a Timoshenko beam is considered, and damage is assumed as a stiffness loss in some elements. Damage locations and extents are identified minimizing some well-known modal parameter based objective functions. It is concluded that modal flexibility is the best among the considered damage indexes. Also, the results show that PSO is an effective optimization approach in structural damage detection.

In this study, the microstructure of a roller material produced by centrifugal casting was characterized and its worn surface was examined after wear test. In the first stage of the study, centrifugal casting was used to produce cast iron based roller material. The cross-section of cast matrix was examined using light and scanning electron microscopy after metallographic preparations. In the second stage, ‘ball-on-disc’ type tribometer was used to investigate the wear behaviour of the cast part under dry sliding condition. In order to observe the effect of loading force, the samples were subjected to 10 N, 30 N and 50 N load and the total sliding distance was selected as 500 m. After wear tests, all the worn surfaces were examined using both light and scanning electron microscopy. It is concluded that (i) the roller had pearlitic cast iron matrix having nodular graphite and eutectic carbide, (ii) worn surfaces exhibited typical abrasive and partial adhesive wear tracks, (iii) as the loading force increased the friction coefficient in addition to weight loss of cast iron matrix increased.

In this study, effects of Co as an alloying element and different heat treatments processes on the properties of DIN 1.3243 and 1.3343 were investigated. Austenitising and tempering temperatures are critical parameters for steel hardening. Also, Co has critical effect on mechanical properties of high speed steels. Samples were subjected to two different austenitising temperatures with two tempering temperatures. Effects of process parameters on the mechanical properties and tooling abilities of the specimens were investigated. Specimens were characterized by Rockwell hardness tests and tooling abilities of the specimen were determined by characterizing the number of screws that were fabricated with specimens. According to results of experiments, Co has any effect on the hardness of specimens after the austenitising and tempering processes. Moreover, tool life of the specimens were increased by the higher hardening temperatures, the lower tempering temperatures and the presence of Co as an alloying element, because of the positive effect of Co on the hot hardness and hot strength.

In this study selection of optimum module, shaft diameter and rolling bearing for conical gear has been done using genetic algorithm (GA). GA, is a novel stochastic method of optimization. GAs are based on the principles of natural selection and evolutionary theory. Objective function was optimized for the design variables between determined boundary values. The GA was constrained by taking into account the power, moment, velocity, wall thickness and bearing distances. Tooth strength and surface crush were considered to be design constraints for module optimization. The other algorithm constraints are maximum bending and torsion moments for shaft optimization, and working life for bearing optimization.

The current practice of assessing the efficiency of recovery of magnetite is represented by Davis tube tests based on magnetic induction. 2 nd factorial design is used for the parametric study of the magnetic separation, because the classical approach is a tedious method. Factorial design is the most efficient way to explore the combinations of variables, because it considers every observation and uses only the most necessary observations. The results of the factorial experiments were used to identify the variables having a significant effect on magnetic recovery. The main objective of this work is to upgrade the iron ore using the Davis tube magnetic tester. It is also intended to study the most important operating parameters affecting the separation process. Among these are the feed size (μm), current intensity (A), tube oscillation (rpm), tube inclination (degree) and wash water rate (l/min). Consequently, the best fit relation can be expressed mathematically as: Y = 58.99 + 7.25X + 4.56I — 1.49O — 2.19W — 1.84S.

Hazardous liquids, liquid explosives and flammable liquids are characterized by means of terahertz time domain spectroscopy (THz-TDS) in analogy to existing non-destructive testing (NDT) strategies. Various polar liquids (alcohols, acetone, hydrogen peroxide, nitro methane) and non-polar aircraft and automobile fuels as well as organic solvents are characterized in the practically relevant, non-contact and non-destructive reflection geometry in the time domain. Absorption coefficients and indices of refraction of a representative set of these liquids are investigated in the spectral range between 0.1 THz and 1.1 THz in transmission configuration by two different set-ups either suitable for strongly or weakly absorbing liquids.