Precipitation hardening of Cu – Ti – Zr alloys

Abstract

The influence of age hardening temperature and time on the hardness, tensile properties, electrical conductivity, and microstructure of Cu – 4Ti – 0.1Zr and Cu – 3Ti – 0.1Zr alloys has been investigated. The resulting microstructure of these alloys suggests that zirconium addition prohibited the formation of compositional modulations in the solution treated condition. These alloys exhibited maximum hardness and strength on peak aging at 450°C for 24 h by the formation of a coherent and metastable Cu₄Ti phase (β') in modulated structure while overaging occurred by the formation of equilibrium phase β-Cu₃Ti. The electrical conductivity of both the alloys increased moderately on aging. Unlike in an earlier study of binary Cu – Ti and some ternary Cu – Ti – X alloys, overaging did not cause any discontinuous precipitation in the Cu – Ti – Zr alloys investigated. Modulated structure formed on peak aging persisted on prolonged aging at 450°C for 80 h or at 500°C for 8 h.     

Compositions of Two Morphological Forms of β-Si6 – zAlzOzN8 – z

Analysis of experimental data on the formation of -sialon (-Si_{6 – z} Al _z O _z N_{8 – z} ) at high temperatures (1300–1500°C) indicates that two morphological forms—fibers and spherical particles—differ in chemical composition:z = 3.58 in the fibers and 2.60 in the spherical particles. The formation of fibers is assumed to follow the whisker growth mechanism, while the spherical particles are likely to grow via diffusion.     

Effect of minor cerium additions on microstructure and mechanical properties of cast Al – Cu – Mg – Ag alloy

Abstract

A series of cast Al – Cu – Mg – Ag based alloys with minor cerium additions have been investigated using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. It was found that increasing the cerium content from 0 to 0.45 wt-% increased the tensile strength at the test temperatures of 25°C and 300°C. The high strength of the casting alloys with cerium is attributed to the refined grains and the high density of fine ω precipitates. However, the addition of 0.2 wt-%Ce to the alloy with 0.25 wt-%Ti induced a detrimental effect on the mechanical properties. The cause of this was found to be the formation of the intermetallic compound Al_x Ti₆ Ce₃ Cu.     

Preparation and Properties of Pb1 – xSnxTe1 – ySeyEpilayers

Pb_{1 – x} Sn _x Te_{1 – y} Se _y layers lattice-matched with KCl and BaF₂are grown by liquid-phase epitaxy. Epilayer compositions and growth temperatures are determined at which p- and n-type materials can be obtained without doping. The composition dependences of the Hall coefficient and carrier mobility are analyzed.     

Obsolescence – A review of the literature

Technology progress and fierce competitiveness between manufacturers creates intense pressues to innovatively develop and sell new products. These products could be household or industrial items, such as telephones, computers, machines, robots, unmanned aerial vehicle (UAV), motors, industrial processes, electronic devices, tools, and spare parts in general. The technological progress implies the use of the word “obsolescence.” The new products have higher performance metrics compared to the older units, such as reliability, resilience, memory capacity, improved material, precision, artificial intelligence, lower energy consumption, ergonomics, and safety. Therefore, obsolescence became a paradox in our daily life and industry. This paper presents a literature review of the main published works on obsolescence (1976–2020). Its typologies, consequences and replacement strategies are illustrated.     

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract

The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm^-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm^-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmission electron microscopy were used for microstructural characterisation of the materials. Precipitation of the second phase was observed to dominate in deformation bands. The alloy showed evidence of discontinuous precipitation, particularly when the alloys were cold rolled before aging. The onset of discontinuous precipitation led to a drastic deterioration in hardness of the alloys. The precipitation behaviour of the alloy is discussed in the light of microstructural characteristics associated with various processing conditions of the alloy.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 1 – Microstructural analysis

Abstract

Specimens of 16Cr - 5Ni - 1Mo stainless steel were solution treated at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, optical microscopy, scanning (SEM) and transmission (TEM) electron microscopy, and X-ray diffraction examinations were conducted. The microstructure of all aged specimens was found to consist of martensite with variable fractions of δ ferrite and reversed austenite. Very fine precipitates of Mo carbides were revealed in the specimens aged at 475 ° C. The specimens aged at 625 ° C showed a decrease in the dislocation density and a high volume fraction of austenite and precipitation of Fe₂Mo Laves phase was detected by X-ray analysis. Above 625 ° C, Cr₂₃C₆ and TiC became the predominate carbides heterogeneously precipitated in the martensitic matrix. Partial transformation of reversed austenite to unaged martensite was observed at temperatures above 625 ° C.     

The railway accident of Eschede – technical background

In 1998 a very severe railroad accident occurred in Germany. The case went to court for negligent homicide after a preliminary investigation had been performed. The accident had been caused by fracture of a wheel and the manufacturer of the wheel and the railroad company were accused. The defendants engaged a number of experts to investigate the different technical aspects of the accident for their defence. In spring 2003 the court decided to employ an unique procedure, to hear all experts consecutively to get the best possible overview of the different opinions and possibly find the real cause of the accident. After the court had heard the testimony of these 13 experts from 5 different countries it decided to discontinue the case since the guilt of the accused was deemed to be very small, if there was any guilt at all and that further technical investigations and expert testimony would most probably bring the court no nearer to a conviction. A failure analysis proper was not the subject of the court procedure and therefore a complete investigation was not carried out. The result of the hearing was in the opinion of most experts, that the accident could not be explained by the results of the investigations performed. Rather a singular incident or technological material phenomenon could have initiated the fatigue crack, which then caused the accident. Since all realistic aspects of the accident had been thoroughly investigated by the experts, only speculations on such incidents or phenomena were possible.     

Tribology of electroless nickel coatings – A review

Electroless coating is different from the conventional electrolytic coating as the former does not require any electricity for its operation. The advantages include uniform coating and also nonconductive materials can be coated. Electroless nickel coatings possess splendid tribological properties such as high hardness, good wear resistance and corrosion resistance. For this reason, electroless nickel has found wide applications in aerospace, automobile, electrical and chemical industries. Quest for improved tribological performances has led many researchers to develop and investigate newer variants of electroless nickel coatings like Ni–W–P, Ni–Cu–P, Ni–P–SiC, Ni–P–TiO₂, and so on. Also the enhancement of tribological characteristics through modification of the coating process parameters has remained a key point of interest in researchers. The technological advancement demands the development of newer coating materials with improved resistance against wear and tear. Electroless nickel has shown huge potential to fit in that space and so the study of its tribological advancement deserves a thorough and exhaustive study. The present article reviews mainly the tribological advancement of different electroless nickel coatings based on the bath types, structure and also the tribo testing parameters in recent years.     

Influence of the surface mechanical pulsed treatment on the oxidation of Fe – 0.2C – 13Cr – 0.3Si steel in lead melts

We study the influence of mechanical pulsed treatment (MPT-1) on the corrosion resistance of Fe – 0.2C – 13Cr – 0.3Si steel in a lead melt containing 1.3 · 10^{– 3} wt.% of oxygen at a temperature of 550°C for 1000 h. It is shown that the MPT promotes the formation of micro- and macrodefects in the subsurface zone of the specimens, which intensifies the process of oxidation of steel. The oxidation resistance of steel after MPT-2 and MPT-3 (with adding aluminum and silicon) is attained as a result of the formation of a hardened zone with nanocrystalline structure and large lengths of grain boundaries intensifying the diffusion of chromium into the oxide films.     

Energy-conserving integration of constrained Hamiltonian systems – a comparison of approaches

In this paper known results for continuous Hamiltonian systems subject to holonomic constraints are carried over to a special class of discrete systems, namely to discrete Hamiltonian systems in the sense of Gonzalez [6]. In particular the equivalence of the Lagrange Multiplier Method to the Penalty Method (in the limit for increasing penalty parameters) and to the Augmented Lagrange Method (for infinitely many iterations) is shown theoretically. In doing so many features of the different systems, including dimension, condition number, accuracy, etc. are discussed and compared. Two numerical examples are dealt with to illustrate the results.     

Adhesion of thermal barrier coatings – the development of metastable alumina

Abstract

The adhesion of thermal barrier coatings (TBCs) is dependent upon the characteristics of the thermally grown oxide (TGO) that forms between the TBC and the corrosion resistant bond coat. Work has been carried out to investigate the properties of the TGO as a function of ageing treatments using piezospectroscopy. Residual stress maps were generated for an electron beam physical vapour deposited (EB-PVD) TBC which showed a large variation in residual stress over the surface of a coated sample. The two peaks generally associated with a alumina (R1 and R2) frequently appear as doublets with a high and low stress component. In addition, the presence of a metastable θ alumina was detected in aged samples. It is believed that these observations can be related to incipient spallation of the TBC. The development of residual stress and the metastable oxide have been studied and correlated with the spallation behaviour of the TBC.     

Predicting the service-life of concrete structures – Limitations of simplified models

North American civil infrastructure systems are deteriorating. Roads, bridges, overpasses, marine and airport facilities are all impacted. The primary causes of premature concrete deterioration are harsh climatic conditions and chemical attacks, particularly exposure to winter de-icing salts and seawater. Given the growing concern for concrete degradation, numerous computer-assisted tools have been developed to assist engineers in the prediction of the service-life of structures. Many of these models are based on simplified equations that significantly restrict the scope of their application. The limitations of these approaches for the design of new construction and rehabilitation of existing structures are discussed. The theoretical assumptions at the basis of these models are first reviewed. Special attention is paid to the consequences of these simplifying assumptions on the reliability of the models. The difficulties of using these simplified models for the treatment of actual structures exposed to natural conditions are then discussed.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 2 – Mechanical property characterisation

Abstract

Mechanical property characterisation has been carried out on specimens of 16Cr - 5Ni - 1Mo stainless steel, subjected to various aging cycles. The heat treatment cycles involved solution treatment at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, tensile, hardness, impact, and creep tests were conducted. Specimens aged at 475 ° C exhibited maximum values of tensile strength and hardness with minimum values of ductility and impact toughness, while specimens aged at 625 ° C had maximum values of impact toughness and ductility. The results were correlated with the microstructural data presented in Part 1 of this study. Softening of the martensitic matrix at 625 ° C occurs as a result of the elimination of internal stresses, the decrease in the dislocation density, and the high volume fraction of austenite which lead to the drop in values of tensile strength and hardness. The results of the study reveal that aging at 550 ° C for 4 h gives the optimum combination of strength, hardness, ductility and toughness for this steel.     

Mechanical alloying – the development of strong alloys

Abstract

Mechanical alloying is a solid-state process for making alloys by high-energy milling, under conditions such that constituent powders are repeatedly fractured and welded together and ever more intimately mixed. After subsequent consolidation at elevated temperature, the alloys can be shaped by rolling, forging, and machining. The process is used to incorporate a fine dispersion of ceramic particles. Mechanically alloyed nickel-base superalloys, combining a dispersion of yttria with conventional precipitation strengthening, have achieved higher strength at 900–1100°C than directionally solidified and single-crystal alloys, and are being used for gas-turbine vanes and blades. Mechanically alloyed ferritic stainless steel, with outstanding strength and corrosion resistance at temperatures as high as 1300°C, has been produced as sheet, tube, plate, rings, and forgings. Mechanically alloyed aluminium alloys also offer higher strength, e.g. in as-forged thick sections of Al–Mg–Li alloy.

MST/567     

Hours-per-vehicle controlling – the renaissance of staff productivity

In the global automobile industry, the Hours-Per-Vehicle factor (HPV) is turning more and more into a key indicator for personnel productivity analysis of a production plant. HPV rankings are compiled and personnel goals are derived from comparison of HPV benchmarks. Besides program units and the budget, HPV is advancing to be one of the dominant controlling indicators. Against this background, there is an increasing demand for effective HPV controlling. The major task of such controlling is to ensure the required transparency for the influencing variables as well as to recommend measures to improve personnel productivity. In this context, HPV controlling is not just to be incorporated in the existing target and controlling landscape, but also into existing personnel productivity improvement processes. This article takes up these requirements and demonstrates approaches to a solution. Moreover, it describes the potential and also the limits of HPV applications.     

The penetration of rigid long rods – revisited

The penetration process of rigid long rods with different nose shapes (ogive, spherical, conical and flat) is analyzed through a series of 2D numerical simulations. Aluminum and steel targets with different strengths (and large dimensions) are used to follow the deceleration process of these rods from impact, at different velocities, to the final penetration point. We find that for low impact velocities the deceleration of these rods is practicably constant, depending only on the strength of the target and the nose shape of the rod. Above a threshold (critical) impact velocity rod deceleration becomes velocity dependent due to the inertial response of the target. These critical velocities depend on the strength of the target and the nose shape of the rod. These observations led us to propose a simple penetration formula which accounts very well for penetration depths data for rigid steel rods with different nose shapes, impacting various aluminum targets at velocities up to about 1.5 km/s. For higher impact velocities, where the dynamic (inertial) contribution to the target resistance is important, we find good agreement between our model predictions and the simulation results for final penetration depths.     

Effect of thermal aging on pitting corrosion resistance of 16Cr – 5Ni – 1Mo precipitation hardening stainless steel

Abstract

Specimens of precipitation hardening 16-5-1 stainless steel were solution treated at 1050°C for 1 h followed by aging at temperatures in the range 400 – 750°C for various holding times (1 – 16 h). After heat treatment, two types of corrosion test (accelerated and immersion testing) were conducted in 6% ferric chloride solution. The results showed that the pitting corrosion resistance was affected by austenite content, δ ferrite and precipitation of molybdenum and chromium carbides. Three critical temperature ranges were identified, which were related to the phases formed: (a) high corrosion rate at 475°C (δ ferrite and Mo₂ C); (b) low corrosion rate at 550 – 625°C (reversed austenite and Laves phase); (c) intermediate corrosion rate at 750°C (Cr₂₃ C₆ and TiC). The morphology of the pitting was dependent on the form of the δ ferrite and carbides.     

Visualizing Properties of Comprehensive SAGBI Bases – Two Examples

This note presents two examples for the visualization of finiteness and size properties of lexicographical comprehensive SAGBI bases for polynomial invariants of conjugates of the alternating and symmetric group in three variables. Received: June 7, 2000; revised version: July 24, 2001