Abstract Glass-to-metal seals are important in hermetic electrical feedthroughs for high-temperature and high-pressure applications. Traditionally, glass-to-metal seals are created using a high temperature furnace with controlled pressure and atmosphere. Current manufacturing techniques for glass-to-metal seals require precise fixturing (limiting unitization) and face restrictions in terms of the coefficient of thermal expansion for the glass/metal system. This paper explores the potential to use a laser to locally heat the glass as the first step toward the additive manufacturing of glass to metal seals. Studies are conducted fusing both frit and preforms under ambient conditions. The effects of process parameters on the process are quantified. The paper shows the potential of the process using Selective Laser Melting equipment, which can lead to greater flexibility for glass-to-metal seals with respect to geometry, materials, and spatially varying properties.

Metal matrix nanocomposites (MMNCs) are anticipated to offer significantly better performance than existing superalloys for additive manufacturing (AM). However, traditional methods of preparing MMNC powder, such as high-energy ball milling, usually involve high cost and high energy consumption. This paper reports experimental results on a novel method to prepare MMNC feedstock powder. Nickel/alumina MMNC powder was successfully produced using electroless plating, containing a high fraction (66 vol. %) of alumina nanoparticles. Then, the MMNC powder was compacted into a disk shape with a hydraulic press and sintered with a tube furnace. After sintering at 1400 °C for 4 hours, the MMNC had a density of 4.16 g/cm 3 . Scanning electron microscopy observation, and X-ray diffractometry and energy-dispersive X-ray spectroscopy analysis were conducted on the sintered Ni/Al 2 O 3 disk. As the alumina nanoparticles were added to nickel, an increased microhardness of HV 0.5 189 was obtained.

Surface hardening was performed by laser surface remelting of AISI H13 tool steel samples using a high power fiber laser. The surface hardened samples were exposed to different tempering temperature of 500°C, 700 °C and 900 °C in a furnace for one hour and brought back to room temperature in still air and by water quenching. Changes of the laser remelted and hardened layer were investigated in terms of microstructure and hardness before and after exposure to different tempering temperatures. Laser remelting caused mainly dendritic microstructure at the top layer but the dendritic structure of the remelted layer got altered after tempering at high temperatures. Air and water quenching caused almost similar result during tempering of laser remelted layer. The microhardness variations along depth after tempering at different temperatures indicates that the surface hardening imparted by laser remelting remains almost intact up to 700 °C but gets destroyed at 900 °C. Although the experimental temperature limits gives approximate threshold values, but it provides a clear indication of a safe limit for laser surface hardened components in high temperature applications like hot-forging dies and friction stir welding tool, etc.

Non-combustible aluminum composite panel is a new type of green building and decoration material with high security. However, during its manufacturing process, the incongruity of temperature cyclings between a series of air circulating tempering furnaces on the production line may cause a serious negative impact on the stability of product quality. In this paper, a model of the temperature control system of a tempering furnace was built at first by applying parameter identification technique to the off-line data of the furnace. Then, an approach based on online parameter identification and model predictive control was proposed to solve the dilemma that the specific temperature range of one single tempering furnace and the temperature cyclings coordination of multiple tempering furnaces can not be attained at the same time when using PID or On-Off control method. A method was presented to optimize the phase difference between the temperature cyclings of differents furnaces’ to lower the fluctuation of product quality. Finally, experiments are used to demonstrate the descent in fluctuation using the methods proposed in this paper.

Higher temperature assisted processing of silicon, such as in heat-assisted diamond turning, is often being considered to improve surface integrity. At higher temperatures and under mechanical loading and unloading, caused by the moving tool, silicon deforms plastically often in association with occurrence of phase transformations. This paper investigates such phase transformations in rotational scratching of single crystal (100) p-type silicon with a conical diamond tool under various furnace-controlled temperatures ranging from room temperature to 500 °C and at scratching speeds comparable to that used in the diamond turning process (1 m/s). Phase transformation study, using Raman spectroscopy, at various crystal orientations, show differences in phases formed at various temperatures when compared to that reported in indentation. The tendency to form phases is compared between scratched and diamond turned surfaces at room temperature, and also with that reported at low scratching speeds in the literature. Analysis of depths of the scratched groove indicates that that at temperatures beyond a certain threshold, plastic deformation and significant elastic recovery may be causing shallow grooves. This study is expected to help tune heat-assisted diamond turning conditions to improve surface formation.

Applications of the induction hardening process have been gradually increasing in the heat treatment industry due to its energy efficiency, process consistency, and clean environment. Compared to traditional furnace heating and liquid quenching processes, induction hardening is more flexible in terms of process control, and it can offer improved part quality. The commonly modified parameters for the process include the inductor power and frequency, heating time, spray quench delay and quench severity, etc. In this study, a single shot induction hardening process of a cylindrical component made of AISI 4340 is modeled using DANTE ® . It is known that the residual stresses in a hardened steel component have a significant effect on high cycle fatigue performance, with higher magnitudes of surface residual compression leading to improved high cycle fatigue life. Induction hardening of steel components produces surface residual compression due to the martensitic transformation of the hardened surface layer, with a high magnitude of compression preferred for improved performance in general. In this paper, a preheat concept is proposed with the induction hardening process for enhanced surface residual compression in the hardened case. Preheating can be implemented using either furnace or low power induction heating, and both processes are modeled using DANTE to demonstrate its effectiveness. With the help of computer modeling, the reasons for the development of residual stresses in an induction hardened part are described, and how the preheat can be used to improve the magnitude of surface residual compression is explained.

Fabricating metal matrix composites (MMCs) through laser assisted additive manufacturing (LAAM) has attracted much attention in recent years. This is because the traditional metal components produced by LAAM are usually inferior to the counterparts produced by conventional manufacturing processes, reflected by porosity, lower density, and thus poorer mechanical properties and service performance. Adding reinforcements to metal matrix in LAAM process can alleviate the challenge. Also, for components produced by LAAM processes, post treatment is often required to further strengthen the material, reduce residual stress, or clean off surface for dimensional accuracy. However, research regarding how post treatment affects the microstructure and mechanical properties of LAAM-produced MMCs is still very rare in literature. In this study, a nano-TiC reinforced Inconel 718 composite is prepared using selective laser melting (SLM) technique. Various post heat treatment processes have been adopted to investigate their effect on final product properties. The motivation is that Inconel 718 is a Ni-based superalloy, whose full potential is explored in heat treatment after manufacturing processes. A composite with 0.5 wt.% nano-TiC addition is prepared. Three levels of solution temperatures at 940, 980, and 1020 °C (for 1 hr) or one level of annealing temperature at 1100 °C (for 1 hr) are adopted for the treatment, combined with the standard two-step aging (720 °C, 8 h, furnace cooling + 620 °C, 8 h, air cooling) on both the MMC and unreinforced Inconel 718 materials. Scanning electron microscopy (SEM) observation is conducted to analyze the microstructure of the composite and understand the reinforcing mechanism. Tensile tests are conducted to evaluate the tensile properties. It is discovered that compared with the pure Inconel 718 by SLM, the Inconel 718-TiC MMC exhibits improved ultimate tensile strength for both as-built and solution/annealing treated conditions. Microscopy observation shows that the dendritic structures of Inconel 718 is remarkably refined by the TiC particles in as-built samples, and grain coarsening is largely inhibited by the TiC particles for solution/annealing treated samples. For both reinforced and unreinforced Inconel 718, dissolving of Laves phase and precipitation of δ phase is observed, but annealing at 1100 °C is not favorable for the formation of δ phase. Aging treatment significantly increases the UTS values for both type of material. Moreover, the strengthening effect of added nano particles becomes less significant in the aged condition, due to the precipitation of γ′ and γ″. Future work includes the process parameter optimization, and further evaluation of other mechanical properties.

Quenching is an important part of the heat treatment process for strengthening medium and high carbon steels. In the heat treatment cycle, the metal is heated to a desired temperature (above the eutectoid temperature) in the furnace and then cooled in a fluid medium such as water, brine, oil or air. Depending on the cooling rate, the mechanical and metallurgical properties of the metal can be altered in order to achieve the specific design parameters that are required by the part. The process in which the metal is cooled rapidly is termed the quenching process. Due to rapid cooling in a medium, such as water, brine, or oil, the quenching process produces an audible sound signature, as well as, acoustic emissions. In this paper, W1 tool steel is investigated through the use of a beam former that is equipped with 32 microphones. Using this device, it is demonstrated that the audible sounds that are produced when quenching depend on the heat treatment temperature and the size of the specimen.

Hot forming of ultra high strength steel is an advanced forming technique which can not only represent the best solution to increasing the strength-to-mass ratio of sheet components, but also meet the need of higher passive safety and weight reduction. Based on independently developed mass production line of hot forming, its key forming and quenching technique and relative equipments are proposed and described, including multi-step and one-step method, die manufacturing with cooling system, continuous heating furnace and integrated manufacturing system composed of the advanced interdisciplinary technology of machining, electronic control, material and chemical engineering. Then the automobile body components are produced by the developed equipments of hot forming and moreover their mechanical properties are investigated. The typical tensile curve of the quenched components shows that the yield stress of the hot forming component is over 1000MPa, and the strength limitation is over 1600MPa. The three-point bending testing of the part is implemented. These experimental results indicate the validity of the developed technique and equipments.

Monitoring and control of thermomechanical parameters in tooling materials are imperative for improving the fundamental understanding, reliability and workpiece quality of material removal processes. Polycrystalline cubic boron nitride (PCBN) tools are being used heavily in machining of low carbon steel and superalloys. These processes are very sensitive to variation in local machining conditions and there lacks a thorough understanding of fundamental thermomechanical phenomena which can lead to abrupt tool failures. Existing sensors for monitoring machining conditions are not suitable for precision process control as they are either destructively embedded and/or do not possess the necessary spatial and temporal resolution to monitor temperature during machining effectively. This paper presents a novel approach to obtain temperature data from a close distance to the tool cutting edge. An array of 9 micro thin film thermocouples, fabricated using standard microfabrication methods, has been embedded into a PCBN cutting tool using a diffusion bonding technique. Scanning electron microscopy (SEM) was performed to examine material interactions at the bonding interface and determine optimal bonding parameters. The sensors were statically and dynamically characterized using a tube furnace and rapid laser heating, respectively. They exhibit good linearity, sensitivity and very fast response time. The instrumented PCBN inserts were applied in machining experiments. Being embedded into the tool at a total distance of only 260 μm from the cutting edge, the micro sensors enabled the detection of local cutting temperature changes caused by interrupted machining. The data obtained during cutting demonstrate the functionality of the tool-embedded micro thermal sensors and their value for fast, accurate and reliable monitoring and control of machining processes.

Currently there is no adequate bone replacement available that combines a long implant life with complete integration and appropriate mechanical properties. This paper reports on the use of human mesenchymal stem cells (MSCs) to populate porous bioceramic scaffolds produced by selective laser sintering (SLS) to create bespoke bioactive bone replacement structures. Apatite-wollastonite glass ceramic was chosen for use in this study because of its combination of excellent mechanical and biological properties, and has been processed using an indirect SLS approach. Process maps have been developed to identify process conditions for the SLS stage of manufacture and an optimised furnace cycle for the material has been developed to ensure that the required material phases for bioactivity are present in the manufactured scaffold. Results from tissue culture with the MSC’s on the scaffolds (using confocal and scanning electron microscopy) show that MSCs adhere, spread and retain viability on the surface, and penetrate into the pores of apatite wollastonite (A-W) glass ceramic scaffolds over a 21 day culture period. The MSC’s also show strong indications of osteogenesis, indicating that the MSC’s are differentiating to osteoblasts. These results indicate good biocompatibility and osteo supportive capacity of SLS generated A-W scaffolds and excellent potential in bone replacement applications.