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961.
962.
The need for new, improved solder alloys and a better understanding of reactions during the soldering process grows steadily
as the need for smaller and more reliable electronic products increases. Information obtained from phase equilibria data and
thermodynamic calculations has proven to be an important tool in the design and understanding of new lead-free solder alloys.
A wide range of candidate alloys can be rapidly evaluated for proper freezing ranges, susceptibility to contamination effects,
and reactions with substrate materials before the expensive process of preparing and testing candidate alloys is initiated. 相似文献
963.
Sang Chul Seo Hyun Jung Kim Byung Ho Park Kwang Suk Son Sung Keun Lee Sun Bae Kang Donggyu Kim 《Metals and Materials International》2006,12(3):273-277
In a continuous casting steelmaking operation, the surface of a slab is under a condition that can be characterized as high-temperature,
low-cycle fatigue in which the tensile and compressive stress is repeatedly developed. For this reason, for the evaluation
of the hot ductility of a slab, considering the fatigue deformation is more feasible before a tensile or compressive test.
In this study, the effects of low-cycle fatigue on the hot ductility of steels with a carbon content of 0.06–0.8 wt.% are
investigated at various temperatures. For a carbon content of 0.06%, there were no significant differences between the RA
values from a simple tensile test and those from a tensile test after fatigue deformation. The tendency of ductility deterioration
with fatigue deformation is evident in 0.1 %C steel, and is due to the deformation-induced ferrite film that forms around
the prior austenite grain. Conversely, high carbon steel containing 0.8 %C did not show a recovery of hot ductility in a low
temperature region, and the specimen on which the tensile was measured after fatigue showed a higher hot ductility in the
low temperature region, which is thought to result from the pearlite refinement effects. As the results obtained in this work
showed noticeable differences in the hot ductility of carbon steel through the test conditions, it is suggested that for more
accurate data, fatigue deformation be adopted in which the temperature range in an unbending operation is determined in the
steelmaking factory. 相似文献
964.
Terry C. Lowe Ruslan Z. Valiev 《JOM Journal of the Minerals, Metals and Materials Society》2004,56(10):64-68
Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive
properties. Today, SPD techniques are rapidly developing and are on the verge of moving from lab-scale research into commercial
production. This paper discusses new trends in the development of SPD techniques suchas high-pressure torsion and equal-channel
angle pressing, as well as new alternative techniques for introducing SPD. The paper also contains a comparative analysis
of SPD techniques in terms of their relative capabilities for grain refinement, enhancement of properties, and potential to
economically produce ultrafine-grained metals and alloys.
For more information, contact Terry C. Lowe, Science and Technology Base Programs, Los Alamos National Laboratory, Los Alamos,
NM 87545; (505) 667-7824; fax (505) 665-3199; e-mail tlowe@lanl.gov. 相似文献
965.
Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds 总被引:1,自引:0,他引:1
K. Narayan Prabhu Bheemappa Chowdary N. Venkataraman 《Journal of Materials Engineering and Performance》2005,14(5):604-609
Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated
cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were
instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history
at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the
one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided
cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell,
which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence
of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal
stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared
with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall
thickness and increase in the casting thickness. 相似文献
966.
Wen-Fung Wang 《Journal of Materials Engineering and Performance》2007,16(5):533-538
Two types of Hoganas iron powders—sponge (NC), and highly compressible (SC) were investigated. These specimens were compacted
with a pressure of 300, 400, 500, 600, and 700 MPa, before sintering in a production belt-type furnace. Steam treatment of
the specimens was at 570 °C for 30 min. The sintered density and as-sintered hardness increase with increasing compaction
pressure, and are significantly influenced by the powder structural characteristics. During steam treatment the type of powder
and compaction pressure have an important influence on the extent of pore closure and weight gain. The maximum hardness was
obtained for the components compacted at a pressure of 500 MPa for both groups of iron powders. Surface pore closure and oxidation
resistance of the steam-treated components are improved with increasing compaction pressure. 相似文献
967.
Young-Wook Kim Yong-Seong Chun Ji Yeon Park Woo Seog Ryu Dong-Soo Park 《Metals and Materials International》2007,13(3):197-200
A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated.
The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes
at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling
the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of >98%. The 2D
SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength. 相似文献
968.
D. S. van Vuuren A. D. Engelbrecht T. D. Hadley 《JOM Journal of the Minerals, Metals and Materials Society》2005,57(10):53-55
The value chain of titanium products shows that the difference between the cost of titanium ingot and titanium dioxide is
about $9/kg titanium. In contrast, the price of aluminum, which is produced in a similar way, is only about $1.7/kg. Electrowinning
of molten titanium from titanium dioxide is therefore believed to have significant potential to reduce the cost of titanium
products. The process is hampered by the high operating temperatures and sophisticated materials of construction required;
the high affinity of titanium for carbon, oxygen, and nitrogen; and physical and chemical properties of the different titanium
oxide species when reducing titanium from Ti4+ to metallic titanium.
For more information, contact D.S. van Vuuren, CSIR, Materials and Manufacturing Technology Department, Meiring Naude Road,
Pretoria, Gauteng 0181, South Africa; +27 12-841 2375; fax +27 841 2135; e-mail dvvuuren@csir.co.za. 相似文献
969.
Design of forging process variables under uncertainties 总被引:4,自引:0,他引:4
Jalaja Repalle Ramana V. Grandhi 《Journal of Materials Engineering and Performance》2005,14(1):123-131
Forging is a complex nonlinear process that is vulnerable to various manufacturing anomalies, such as variations in billet
geometry, billet/die temperatures, material properties, and workpiece and forging equipment positional errors. A combination
of these uncertainties could induce heavy manufacturing losses through premature die failure, final part geometric distortion,
and reduced productivity. Identifying, quantifying, and controlling the uncertainties will reduce variability risk in a manufacturing
environment, which will minimize the overall production cost. In this article, various uncertainties that affect the forging
process are identified, and their cumulative effect on the forging tool life is evaluated. Because the forging process simulation
is time-consuming, a response surface model is used to reduce computation time by establishing a relationship between the
process performance and the critical process variables. A robust design methodology is developed by incorporating reliability-based
optimization techniques to obtain sound forging components. A case study of an automotive-component forging-process design
is presented to demonstrate the applicability of the method. 相似文献
970.
Nikolaos Petsas Giorgos Kouzilos Giorgos Papapanos Michalis Vardavoulias Angeliki Moutsatsou 《Journal of Thermal Spray Technology》2007,16(2):214-219
The purpose of the present work was the investigation and characterization of the quality of air in a thermal spray industry,
in Greece. The activities that take place in the specific facility, as well as in most other similar industries, include thermal
spraying and several mechanical and metallurgical tasks that generate airborne particles, such as grit-blasting, cutting and
grinding of metallic components. Since the main focus of this work was the workers exposure to airborne particles and heavy
metals, portable air samplers with quartz fiber filters, were used daily for 8 h. Three samplers, carried from different employees,
were used for a period of 1 month. Results showed that both particles and heavy metals concentrations were low, even in the
production site, which was the most susceptible area. The only exceptions were observed in the case of cleaning and maintenance
activities in the thermal spray booth and in the case of spraying outside the booth. The main reason for the low concentrations
is the fact that most of the activities that could produce high-particle concentrations are conducted in closed, well-ventilated
systems. Statistical elaboration of results showed that particles are correlated with Ni, Cu, Co. The same conclusion is extracted
for Fe, Mn. These correlations indicate possible common sources. 相似文献