발간논문

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The kinetics of growth of the gamma prime precipitates in Rene´ 41 have been studied by means of electron microscopy. The coarsening behavior of the gamma prime precipitates was determined as a function of aging time by measuring the particle sizes of samples aged at 760℃, 840℃ and 880℃, respectively. The measured coarsening rates and particle size distributions were in good agreement with the predictions of the Lifshitz-Wagner theory of diffusion controlled coarsening at all aging temperatures examined. The value of the activation energy for the coarsening process was found from the experimental data to be 65.9 ㎉/㏖. Also the merphology of gamma prime precipitates is discussed.

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In order to study the agehardening and metallography of slip characteristics of the heat-treated aluminium-3.4% copper alloy, replica and transmission electron microscopy have been used. After the alloys have been aged at 220℃ and 250℃ they were stretched up to fracture. Their hardness showed single stage aging curve. The θ` phase and G. P. 2 zone were definite platelets and formed on the {100} matrix planes in a Widmansta¨tten pattern. Rough estimates were made on the yield strength of alloys containing intermediate θ` precipitates in the matrix, using a few models for the strength of precipitation-hardened alloys. Slip lines which were found in this experiment are the interpreted in terms of various theories appropriate to each one. It is clearly concluded that slip lines pass through the precipitate particles causing platelets in their path to deform and the age hardening of aluminium 3.4% copper alloy can be explained by considering the internal stress and the precipitate-matrix interfacial energy produced when a dislocation penetrates precipitates in the matrix.

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The effects of additional clement Fe in the range of 0.05-0.16% on G.P. zone formation and ageing phenomena in Al-1.0% Mg₂Si pseudo binary alloy were investigated by means of Vickers microhardness and electrical resistivity measurement. The results obtained were summarized as follows: (1) The G.P. zone formation was delayed in low temperature ageing and the rate of precipitation was increased without G.P. zone formation in high temperature ageing by the additional element Fe. (2) The critical temperature of G.P. zone was 208℃, and it was dropped down by the effect of additional element Fe as 160℃ at the 0.16% Fe content. (3) The hardness of specimens added element Fe were a little higher than that of matrix alloy in the initial ageing time. The above results can be explained by the facts that Fe compounds in the alloy undisolved even at solution treatment temperature decreases the concentration of effective vacancy and solute atom, and also accelerate the growth of precipitate in the alloy.

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It is one of the most important research to study effects of inoculation which add inoculant, very small amount of metal or alloy, into the cast iron melts just before pouring in the mold. Many properities of spheroidal graphite cast iron have been improved by the inoculation. The relation between inoculation and components of melts, mass effect of specimen and spheroidizer used, have been investigated and the important results obtained from the study are summerized as follows. (1) The biggest effect of the inoculation has been obtained in the case of low carbon equivalent, especially low content of silicon in the cast iron melt. (2) The inoculation effects for high carbon equivalent, specially high silicon spheroidal graphite cast iron melt are very small.

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In the previous paper, the author investigated the effect of pressure applied during solidification on the structure and strength in Zn-22% Al alloy. In the present study, wear test was carried out under dry condition in order to investigate the anti-wear properties of Zn-22% Al alloy solidified under various high hydrostatic pressures. The results obtained from this study are summarized as follows: (1) Anti-wear properties of Zn-Al alloy were improved by the pressure applied during solidification. (2) Friction coefficient was not affected by the pressure applied during solidification.

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In this paper are described reactions pertaining to the formation of tri-copper phosphide (Cu₃P) at moderately low temperatures in order to provide informations for the manufacture of suitable copper-phosphorus master alloy without fusion. Primary investigation of heated briquettes of a mixture of copper and red phosphorus revealed that all the products obtained at various temperatures (300∼800℃) had been comprised of no other phosphides than Cu₃P. The rate of phosphidation of copper exposed to phosphorus vapor under various pressures up to 1 atm. have been determined in the similar temperature range. The rate of reaction increased with rising temperature and with increasing pressure of the phosphorus vapor. In general the phosphidation proceeded nearly according to a parabolic rate law. The depth of reaction reached ∼0.5 ㎜ when solid copper at 730℃ was exposed to phosphorus vapor (1 atm.) for an hour. The product formed was a dense layer of Cu₃P, and there appeared not be present appreciably any other form of phosphides.

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The neutralization of wolframate ion, WO₄^=, was studied in the presence of neutral salt. The equilibrium was established quickly for the region smaller than 1.15 of average number of H^+ bound per WO₄^=(Z). For the region of Z>1.15 the potential was found to drift slowly for long time without reaching a stationary value. At the region of Z=1.15 the potential drifted rapidly for tire first one minute after each addition of the acid, and then the rate of the drift was only 0.01 to 0.02 pH unit per minute. The neutralization curve of wolframate shows large potential break in the presence of neutral salt. The inflection point of neutralization curve appears at the point of Z=1.148±0.001 when the potentials were measured two to three minutes later after each addition of acid at the region of slow reaction. Only one or two potential measurements are enough to locate the inflection point at slow reaction range since the inflection point lies at the neighbour of starting point of slow reaction. In the presence of enough neutral salt the potential break was so large that such small changes of potential did not affect the accuracy of the titration. Also the influences of molybdate and carbonate have been studied. Analytical procedure was described for the determination of tungsten in the synthetic mixtures.

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The diffusion of carbon in Ni-Cr-Mo steel teas studied by autoradiography. The alloys were melted using high purity low carbon steel. The high carbon alloys were made by the addition of low-activity C^(14) (diluted to 0.050 m Ci per g). After casting into steel moulds and forging all alloys were homogenized in argon for 24 hrs at 1400℃ or 1280℃. Diffusion couples were welded with Toyoda Frictional Welder. After the diffusion couples were annealed they were sectioned along their cylindrical axes. The faces were exposed to X-ray film for some 12 days. Diffusion coefficients of carbon in 3.0% Ni-0.8% Cr-0.3% Mo steel at various temperatures are 10^(-8)∼10^(-7)㎠/sec. It is concluded that the autoradiographic technique can be effectively used to determine the effect of strong carbide-forming alloying elements on the diffusion rate of carbon in austenite.

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