Material Processing Methods Research Articles

Distributed-Parameter Control of the Heat Source Trajectory in Thermal Materials Processing

In thermal manufacturing processes performed by a localized, sequentially moving heat source, simultaneous regulation of multiple thermal quality characteristics requires real-time control of the temperature field developed through the distributed heat input on the part surface. Such control of the thermal field to a desired distribution employs infrared sensing and feedback of the surface temperature hill, to modulate the torch power and motion in-process. The torch trajectory is guided in real time by an efficient optimization algorithm based on the concept of moving complexes. This distributed-parameter control strategy is developed using a numerical simulation model of thermal processing, and its performance is evaluated experimentally in heat treatment of thin stainless steel plates. The thermal controller is applied to the new scan welding process, in which it drives the torch in a reciprocating motion along the weld, yielding a uniform and smooth temperature field, and thus a favorable material structure and mechanical properties. Application of such thermal control to various other material processing methods is also investigated.

Materials processing with high direct-current magnetic fields

Applications of magnetohydrodynamics (MHD) in metals processing, using a constant magnetic field, are now well understood. MHD are widely used to stabilize or to shape a surface, to brake motion, or to suppress random velocities in a liquid metal, and even to develop thermoelectromagnetic convection near a solidification front. Due to progress in superconducting materials and the development of cryogenic technology, constant magnetic fields of high intensity are now available, opening the way to the exploitation of new phenomena that could lead to new methods of materials processing.

Emerging methods for the intelligent processing of materials

Emerging methods, procedures, and performance measures are presented for the design of intelligent materials processing systems that combine both comprehensive new process representations and correspondingly advanced process control systems. The description of these developments is presented in five parts. The first provides the partitioning of global processes into decoupled finite subprocesses for improved accommodation of process nonlinearities with accompanying simplification of control system complexity. The second is sensor/controller/actuator accountability to establish an on-line process variability baseline whose greatest sensitivity is attributable to process measurement limitations. Development three combines multiloop control with decoupled subprocesses for enhanced process disorder reduction and improved likelihood of achieving material parameters of interest. The fourth, closely associated with development three, provides accurate multiloop control compensation by identification of decoupled trapezoidal subprocess models. The fifth presents a process description language of qualitative subprocess influences for augmenting incompletely modeled processes and unmeasurable control elements by supervising the control space to minimize control conflicts and process variability.

Methods of Improving Glow-Discharge-Deposited a-Si1−xGex:H

ABSTRACTWe have studied methods of improving glow-discharge-deposited a-Si1−x Gex :H alloys deposited using silane and germane gas mixtures. Material processing methods studied include (1) varying the substrate temperature from 170° to 280°C, (2) varying the process gas composition and pressure, (3) dilution of the feed gas by hydrogen, argon, or helium, (4) enhancing etching during deposition by adding small amounts of XeF2 vapor into the process gas, and (5) postdeposition annealing and/or hydrogenation.

High Temperature Oxidation of Ni3Al Composites

AbstractAs part of an effort to develop oxidation-resistant metal matrix composites, the influence of reinforcement materials on the oxidation of Ni3Al was studied. Thermogravimetric measurements and microstructural analyses were used to determine the 800°C oxidation behavior of Ni3Al and composites based on this material. The presence of fiber (Al2O3)- or particle (TiN or TiC)- reinforcement material in the Ni3Al increased susceptibility to oxidation as measured by the amount of reacted material, rate constants, and/or extent of internal attack. The orientation of fibers with respect to the free surfaces was found to affect the oxidation behavior by providing, in certain cases, reactive paths along the fiber-matrix interface that led to significant internal penetration. The results suggest that the choice of reinforcement material and the method of materials processing will be important considerations in the design of oxidation-resistant Ni3Al composites. However, ways to minimize the detrimental influence of the reinforcement material on oxidation resistance often conflict with requirements for obtaining attractive mechanical and physical properties of the composite.

Laser surface alloying

Laser alloying is a material-processing method which utilizes the high power density available from focused laser sources to melt metal coatings and a portion of the underlying substrate. Since the melting occurs in a very short time and only at the surface, the bulk of the material remains cool, thus serving as an infinite heat sink. Large temperature gradients exist across the boundary between the melted surface region and the underlying solid substrate. This results in rapid self-quenching and resolidification. Quench rates as great as 1011 KS-l and concomitant resolidification velocities of 20m S-l have already been achieved. What makes laser surface alloying both attractive and interesting is the wide variety of chemical and microstructural states that can be retained because of the rapid quench from the liquid phase. These include chemical profiles where the ‘alloyed’ element is highly concentrated near the atomic surface and decreases in concentration over shallow depths (hundreds of nanometres), and uniform profiles where the concentration is the same throughout the entire melted region. The types of microstructures observed include extended solid solutions, metastable crystalline phases, and metallic glasses.

Laser surface alloying: a bibliography

Laser alloying is a material processing method which utilizes the high power density available from focused laser sources to melt metal coatings and a portion of the underlying substrate. Since the melting occurs in a very short time and only at the surface, the bulk of the material remains cool, thus serving as an intimate heat sink. Large temperature gradients exists across the boundary between the melted surface region and the underlying solid substrate. The result is rapid self-quenching and resolidification. Quench rates as great as 1011 K sec−1 and concomitant resolidification velocities of 20 m sec−1 have already been realized. What makes laser surface alloying both attractive and interesting is the wide variety of chemical and microstructural states that can be retained because of the rapid quench from the liquid phase. These include chemical profiles where the “alloyed” element is highly concentrated near the atomic surface and decreases in concentration over shallow depths (hundreds of nanometers), and uniform profiles where the concentration is the same throughout the entire melted region. The types of microstructures observed include extended solid solutions, metastable crystalline phases, and metallic glasses. This bibliography is a compilation of published work in this area.

Embankment Construction: New Melones Dam

New Melones Dam, located on the Stanislaus River in central California, is a zoned earth and rockfill structure with a maximum height above foundation at embankment centerline of 637 feet and with a volume of about 15.9 million cubic yards. The dam consists of a rolled rockfill embankment with a central impervious core inclined upstream. This paper describes the site geology, foundation treatment, embankment construction procedures, embankment properties and instrumentation. The influence of site conditions and fill requirements on the degree of foundation excavation, surface treatment and grouting patterns are discused. Sources of construction materials and methods of excavation, stockpiling, materials processing and fill placement procedures are described.

Plastics in automobiles at SITEV '81

Abstract In the March 1981 edition of Materials in Engineering (P149) D. Charlesworth ‘Potential use for plastics in Automobiles’, reviewed in terms of materials properties and processing methods the advantages and limitations of plastics in comparison with metals. In order to convince car makers of the potential of plastics, materials suppliers and component manufacturers develop prototype parts which are publicly displayed, often for the first time, at motor shows. The most important of these shows is the International Exhibition of Suppliers to the Vehicle Industry (SITEV). SITEV '81 took place in Geneva and the more significant new applications of plastics to automobile components are reviewed and their likelihood of adaption by the automotive industry assessed in this article by Dr. N.A. Waterman who is a consultant on materials selection to the plastics and automotive industries.

Ultraviolet Radiation in Treatments for Imparting Functional Properties to Cotton Textiles 1

The desirability of developing new methods for the chemical processing of textile materials has encouraged studies of ultraviolet radiation in textile finishing. Wrinkle-resastant cotton and flame- resistant cotton were prepared by processes that include photo-initiated, free-radical reactions resulting from ultraviolet radiation of cotton in the presence of reactive monomers. The influences of variables in the treatments were determined and optimum conditions identified. Other important findings on the chemistry and technology of ultraviolet radiation were observed.