Search results

IN 1946, a short conference on creep in metals was held at the initiative of the National Physical Laboratory. The aircraft gas turbine was then relatively new. It had been developed during the war as a small fighter engine with outstanding power/weight ratio and short life. Since then it has been applied successfully to commercial aircraft and to ship propulsion and its use in power generation is being actively explored. These applications require in general larger engines, longer lives (up to 100,000 hours in many cases), and high thermal efficiency.

The purpose of this paper is to investigate the creep properties of Sn‐0.7Cu composite solder joints reinforced with optimal nano‐sized Ag particles in order to improve the creep performance of lead‐free solder joints by a composite approach.

The composite approach has been considered as an effective method to improve the creep performance of solder joints. Nano‐sized Ag reinforcing particles were incorporated into Sn‐0.7Cu solder by mechanically mixing. A systematic creep study was carried out on nano‐composite solder joints reinforced with optimal nano‐sized Ag particles and compared with Sn‐0.7Cu solder joints at different temperatures and stress levels. A steady‐state creep constitutive equation for nano‐composite solder joints containing the best volume reinforcement was established in this study. Microstructural features of solder joints were analyzed to help determine their deformation mechanisms during creep.

The creep activation energies and stress exponents of Ag particle‐enhanced Sn‐0.7Cu lead‐free based composite solder joints were higher than those of matrix solder joints under the same stress and temperature. Thus, the creep properties of nano‐composite solder joints are better than those of Sn‐0.7Cu solder joints.

The findings indicated that nano‐sized Ag reinforcing particles could effectively improve the creep properties of solder joints. A new steady‐state creep constitutive equation of nano‐composite solder joints was established. Deformation mechanisms of Sn‐0.7Cu solder and nano‐composite solder joints during creep were determined.

In terms of science, technologies and end‐use applications, ‘lead‐free solders’ are a very broad subject. This paper is intended to highlight the key issues of this broad subject for its applications in electronic packaging and assembly. The areas covered include the main thrusts behind the research and development effort, the scientific approaches, economic and practical considerations, and regulatory and legislative perspectives of lead. In addition, this paper will present the new findings as a result of research and development effort on lead‐free solders. Technologically, in view of the current and future needs in interconnecting materials, the first objective of this work is to demonstrate the ability to provide lead‐free solders in lieu of conventional lead‐bearing solders without mandating significant changes in manufacturing processes and/or equipment which have been established and proven in the industry. The second objective is to design the lead‐free solders which are able to offer superior performance to their Sn/Pb counterparts, thus providing solder interconnections with higher reliability and endurance during service life. The fulfilment of these two objectives will concurrently address the two critical technological areas in the field of solders, namely the inherent vulnerability of conventional solders to temperature and stress, and the concerns of toxicity and health hazard of lead. Based on materials principles, ternary and quaternary lead‐free systems are at present being designed. The work conducted thus far demonstrates that two of the designed solder compositions show great promise. In comparison with 63Sn/37Pb eutectic solder, the new lead‐free compositions exhibit superior performance in shear strength, creep resistance and thermomechanical fatigue resistance. This paper will also cover the data in mechanical testings, the summary of microstructure evaluation (with detailed elucidation omitted), and low‐cycle fatigue fractoqraphy examination of the designed lead‐free compositions.

Conventional solder materials are generally low temperature and low strength materials which are particularly vulnerable to temperature and stress. Even under ambient temperature, 298±5°K, the homologous temperature of most soft solder compositions exceeds 0.5. It is therefore anticipated that the properties and behaviour of such solder compositions could alter significantly when they are exposed to temperature change, temperature rise and/or a moderate level of stresses. With the continued innovation and development of microelectronic packages along with the intense global competition, the reliability of solder joints and the quality and yield of making solder joints in production become increasingly important. This research is to address the fundamental material deficiencies of conventional solders in an effort to develop superior solder materials. Several material principles have been considered including both intrinsic material and soldering process approaches. This paper presents the preliminary results of strengthening effects from the intrinsic material approach. The soldering process effects will be presented in a separate paper. The strengthening effects were evaluated by the combined consideration of monotonic shearing, creep and isothermal low cycle fatigue tests. Fatigue fractography and microstructure of the strengthened solder were characterised in comparison with conventional 63Sn/37Pb solder. The results showed that the proprietary solder system possesses a higher monotonic flow resistance as cyclic frequency decreases to 10−4 Hz. Deformation mechanisms and fatigue failure modes are also discussed in this paper.

SEVERAL years before the British and French Governments decided, separately, to initiate feasibility studies into the building of a supersonic transport passenger‐carrying aircraft with an auminium alloy as the main structural material, the Research and Development Division of High Duty Alloys Ltd. began to compare the relative merits of selected Hiduminium alloys in anticipation of this possible new application. It was appreciated that the life requirement, for ecenomic reasons, would be between 20,000 and 30,000 hours and that the saturation skin temperature, due to kinetic heating, at speeds of Mach 2·2 and 2·5 would be about 120° and 150°C, respectively. The Division's considerable experience in the field of developing aluminium alloys for acro‐gas turbine applications for service at temperatures higher than this range, made us optimistic about the possibility of being able to develop a wrought aluminium alloy which would meet all the mechanical property requirements for the construction of a SST aircraft.

For a solution of a problem in practical engineering to be of any value it must be capable of concrete numerical computation at the design stage; and, moreover, it must be such that definite results can be arrived at in a reasonable time. It is seldom necessary for the solution to be exact, since the data and conditions of engineering problems are rarely precise. But what is expected of a solution to a practical problem is that it should give a fairly good approximation to the values observed experimentally or known from experience.

This paper aims to present a broad review of near-a titanium alloys for high-temperature applications.

Following a brief introduction of titanium (Ti) alloys, this paper considers the near-α group of Ti alloys, which are the most popular high-temperature Ti alloys developed for a high-temperature application, particularly in compressor disc and blades in aero-engines. The paper is relied on literature within the past decade to discuss phase stability and microstructural effect of alloying elements, plastic deformation and reinforcements used in the development of these alloys.

The near-a Ti alloys show high potential for high-temperature applications, and many researchers have explored the incorporation of TiC, TiB SiC, Y₂O₃, La₂O₃ and Al₂O₃ reinforcements for improved mechanical properties. Rolling, extrusion, forging and some severe plastic deformation (SPD) techniques, as well as heat treatment methods, have also been explored extensively. There is, however, a paucity of information on SiC, Y₂O₃ and carbon nanotube reinforcements and their combinations for improved mechanical properties. Information on some SPD techniques such as cyclic extrusion compression, multiaxial compression/forging and repeated corrugation and straightening for this class of alloys is also limited.

This paper provides a topical, technical insight into developments in near-a Ti alloys using literature from within the past decade. It also outlines the future developments of this class of Ti alloys.

The purpose of this paper is to present results of laboratory testing work on causes of a service failure/damage to an aircraft turbojet's gas‐turbine blade made of the EI 867‐WD alloy.

The tests comprised comparing the microstructure of a service‐damaged blade with microstructures of specimens drawn from a similar all‐new blade, both subjected to temperatures of different values for different annealing times.

Findings based on the comparison of experimentally gained results of microstructure examination of both the gas‐turbine blades were: the change in the microstructure of a damaged blade results from the growth and cuboidal‐to‐lamellar change of shape of the reinforcing phase γ′ (Ni₃Al); and the size and shape of this phase are comparable to those of the phase γ′ of a new blade subjected to annealing at temperature exceeding 1,223 K for 1 h. The results gained allowed for drawing the conclusion that the damaged turbine blade was operated in the exhaust‐gas temperature exceeding the maximum permissible value of 1,013 K for approximately 1 h in the course of an air mission.

The comparison‐oriented experimental testing work was carried out on a new blade manufactured in the way and from material identical to those of the damaged blade. The applied methodology enables us to gain qualitative results of investigating into the causes of a failure/damage to a gas‐turbine blade.

The presented methodology of identifying (origin‐finding of) a service‐induced damage to a gas‐turbine blade proves helpful in the case of an engine failure, when information on the operating conditions thereof is insufficient.

The paper is an original work by the authors. To the best of their knowledge, the issue has not been found in the literature, approached in this particular way. It has been based on research work on air accidents due to the service‐induced failures/damages to gas‐turbine blades in aircraft turbojet engines.

Unconventional machining processes, particularly ultrasonic vibration cutting (UVC), can overcome such technical bottlenecks. However, the precise mechanism through which UVC affects the in-service functional performance of advanced aerospace materials remains obscure. This limits their industrial application and requires a deeper understanding.

The surface integrity and in-service functional performance of advanced aerospace materials are important guarantees for safety and stability in the aerospace industry. For advanced aerospace materials, which are difficult-to-machine, conventional machining processes cannot meet the requirements of high in-service functional performance owing to rapid tool wear, low processing efficiency and high cutting forces and temperatures in the cutting area during machining.

To address this literature gap, this study is focused on the quantitative evaluation of the in-service functional performance (fatigue performance, wear resistance and corrosion resistance) of advanced aerospace materials. First, the characteristics and usage background of advanced aerospace materials are elaborated in detail. Second, the improved effect of UVC on in-service functional performance is summarized. We have also explored the unique advantages of UVC during the processing of advanced aerospace materials. Finally, in response to some of the limitations of UVC, future development directions are proposed, including improvements in ultrasound systems, upgrades in ultrasound processing objects and theoretical breakthroughs in in-service functional performance.

This study provides insights into the optimization of machining processes to improve the in-service functional performance of advanced aviation materials, particularly the use of UVC and its unique process advantages.

Ceramic materials and glasses have become important in modern industry as well as in the consumer environment. Heat resistant ceramics are used in the metal forming processes or as welding and brazing fixtures, etc. Ceramic materials are frequently used in industries where a wear and chemical resistance are required criteria (seals, liners, grinding wheels, machining tools, etc.). Electrical, magnetic and optical properties of ceramic materials are important in electrical and electronic industries where these materials are used as sensors and actuators, integrated circuits, piezoelectric transducers, ultrasonic devices, microwave devices, magnetic tapes, and in other applications. A significant amount of literature is available on the finite element modelling (FEM) of ceramics and glass. This paper gives a listing of these published papers and is a continuation of the author's bibliography entitled “Finite element modelling of ceramics and glass” and published in Engineering Computations, Vol. 16, 1999, pp. 510‐71 for the period 1977‐1998.

The form of the paper is a bibliography. Listed references have been retrieved from the author's database, MAKEBASE. Also Compendex has been checked. The period is 1998‐2004.

Provides a listing of 1,432 references. The following topics are included: ceramics – material and mechanical properties in general, ceramic coatings and joining problems, ceramic composites, piezoceramics, ceramic tools and machining, material processing simulations, fracture mechanics and damage, applications of ceramic/composites in engineering; glass – material and mechanical properties in general, glass fiber composites, material processing simulations, fracture mechanics and damage, and applications of glasses in engineering.

This paper makes it easy for professionals working with the numerical methods with applications to ceramics and glasses to be up‐to‐date in an effective way.