• Journal of the Korean Society for Heat Treatment
• /
• v.22 no.2
• /
• pp.101-107
• /
• 2009

Effect of isochronic aging on transformation behavior of Ti-50.85at%Ni alloy were investigated by differential scanning calorimeter (DSC). The martensitic transformation temperature increases with increasing annealing temperature until reaching a maximum, and then decreases with further increasing annealing temperature. This can be rationalized by interaction between the distribution of $Ti_3Ni_4$ precipitates and Ni content in the matrix. The R-phase transformation temperature increases with increasing annealing temperature until reaching a maximum, and then decreases with a further increase of annealing temperature. This is attributed to the change of Ni content in the matrix caused by precipitation of $Ti_3Ni_4$. The occurrence of the multiple-stage martensitic and R-phase transformation is attributed to precipitation-induced inhomogeneity of the matrix, both in terms of composition and of internal stress fields.

• Journal of the Korean institute of surface engineering
• /
• v.42 no.5
• /
• pp.246-249
• /
• 2009

Cu-Ti alloys with titanium in the range of 0.5-6.0 wt% were developed to evaluate the effect of the titanium content and heat treatment on microstructure, hardness, and electrical conductivity. The hardness of the Ti-added copper alloys generally increased with the increase in titanium content and hardening was effective up to the 2.5 wt%-Ti addition. Microstructural examination showed that the second phase of $Cu_4Ti$ started to precipitate out from the 3.0 wt% Ti-addition, and the precipitate size and volume fraction increased with further Ti addition. Aging of the present Cu-Ti alloys at $450^{\circ}C$ for 1 h increased the hardness; however, the further aging up to 10 h did not much change the hardness. In the present study, it was inferred that in optimal Ti addition and aging condition Cu-Ti alloy could have the hardness and electrical conductivity values which are comparable to those of commercial Cu-Be alloy.

• Journal of the Korean Society for Heat Treatment
• /
• v.14 no.1
• /
• pp.17-21
• /
• 2001

The effects of Cr content above its solubility limit and thermomechanical treatment on tensile strength and electrical conductivity of Cu-Cr alloys were studied to obtain optimum Cr content exhibiting a high tensile strength without degradation of electrical conductivity. The increase in Cr content above the solubility limit increased tensile strength of Cu-Cr alloys without deterioration of the electrical conductivity. The electrical conductivity was not affected by cold rolling. The electrical conductivity of a Cu-3.5%Cr alloy subjected to cold rolling ${\rightarrow}$ aging treatment ($450^{\circ}C{\times}1hr$) ${\rightarrow}$ cold rolling was equal to that of the alloy subjected to cold rolling ${\rightarrow}$ aging treatment. However, the tensile strength of the alloy subjected to the former thermomechanical treatment was superior to that of the alloy subjected to the latter thermomechanical treatment at all the deformation degrees.

• Journal of the Korean Society for Heat Treatment
• /
• v.33 no.4
• /
• pp.173-179
• /
• 2020

The purpose of this study was to investigate comparatively the microstructural characteristics and hardness of discontinuous precipitates (DPs) in Mg-9%Al alloy, which were formed by continuous cooling (CC) from 678 K to RT and isothermal aging (IA) at 413 K, respectively. In as-cast state, the Mg-9%Al alloy consisted of partially divorced eutectic β(Mg₁₇Al₁₂) particles with a small amount of DPs showing (α+β) lamellar morphology adjacent to the β particles. The DPs formed by CC had interlamellar spacings in a broad range of 0.85~2.12 ㎛ (1.51 ㎛ in average) owing to the various formation temperatures in response to continuous cooling process. Meanwhile, the DPs formed by IA had relatively narrower interlamellar spacings of 0.14~0.29 ㎛ (0.21 ㎛ in average), which is associated with the low and constant formation temperature. Thinner and higher volume fraction of β phase layers were noticeable in the DPs formed by IA. Higher hardness values were obtained in the DPs formed by IA than the DPs formed by CC, which may well be ascribed to the finer lamellar structure and higher β phase content of the DPs formed by IA.

• Journal of Korea Foundry Society
• /
• v.37 no.1
• /
• pp.14-20
• /
• 2017

The microstructure, electrical conductivity and hardness variation of an AZ91-5wt%Sn Mg alloy sample during a solid-solution and aging heat treatment were instigated by optical microscopy, scanning electron microscopy, X-ray diffraction and by Rockwell hardness techniques in this study. The XRD result shows that the main phases in the as-casted alloy are ${\alpha}$-Mg, $Mg_{17}Al_{12}$ and $Mg_2Sn$. From the SEM images of the AZ91-5wt%Sn Mg alloy after the solution treatment, the $Mg_{17}Al_{12}$ phases in the alloy were found to have dissolved into the matrix with an increase in the holding time during the solution treatment, but $Mg_2Sn$ phases were clearly observable. The highest peak hardness of the AZ91-5wt%Sn Mg alloy is 82HRE at an aging temperature of $200^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.10
• /
• pp.917-923
• /
• 2005

In this paper, effect of catalytic configuration on the sensing properties of $SnO_2$ nanoparticle gas sensitive thick film was investigated. Two types of catalytic configuration, mono and binary, were made on the $SnO_2$ nanoparticle. In case of mono catalytic system, $3 wt\%$ Pd or Pt catalyst was doped onto the $SnO_2$ nanoparticle, respectively. In case of binary catalytic system, Pd and Pt was doped simultaneously with concentration ratio of 1:2 to 2:1 onto the $SnO_2$ nanoparticle. After doping, gas sensitive thick film was printed on alumina substrate and heat-treated at 450 to $600^{\circ}C$. Gas sensing properties was evaluated using 500 to 10,000 ppm $CH_4$ gas. As a result, gas sensitive thick film with binary catalytic system showed unstable phenomena that the gas sensitivity was changed according to aging time. In contrary, the mono catalytic system showed relatively stable phenomena despite of aging time. Especially, gas sensitive thick film doped with $3 wt\%$ Pt catalyst and heat-treated at $500^{\circ}C$ showed good sensing properties such as 0.57 of $R_{3500}/R_{1000}$ and very small variation within $3.5\%$ after aging for 5 hours, and response time was very short less than 20 seconds.

• Journal of the Korean Society for Heat Treatment
• /
• v.15 no.6
• /
• pp.260-268
• /
• 2002

The effects of calcium and silicon on microstructure and aging characteristics of AZ91 magnesium alloy during T5 treatment was investigated. The addition of 0.88% calcium or 0.25% silicon to AZ91 alloy made dendrite cell smaller. Especially, silicon is more effectively acted as refinement of the dendrite cell than calcium. It is due to that $Mg_2Si$ precipitated at the dendrite cell boundary or in the matrix during T5 treatment of Si added AZ91 alloy retarded the growth of the secondary phase. In the mean while, without inducing the precipitates containing calcium, calcium was segregated mainly around secondary phase such as $Mg_{17}Al_{12}$ and partially dissolved in ternary eutectic (Mg-Al-Ca) structure. In the AZ91 alloy containing both silicon and calcium, more finely distributed $Mg_2Si$ in matrix homogeneously and much finer microstructure were obtained than those containing silicon or calcium. Hence, An AZ91 containing both silicon and calcium was more effective to retarding the growth of the secondary phase than the other AZ91 alloy such as AZ91 alloy containing silicon or AZ91 alloy containing calcium.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.40 no.2
• /
• pp.43-56
• /
• 2008

The purpose of the experiment was to evaluate the material stability of the paper of the annals of Joseon Dynasty for the conservation purpose and the categories were as listed below : 1. Procuring traditional Hanji and semi-Hanji from different regional hanji paper mill. 2. Artificial accelerated aging treatment to examination its stability (UV irradiation, dry heat) 3. Analysis of optical, physical characteristic. The suitable Hanji for categories would be used as a reconstruction material for the waxel paper in the papers of the annals of Joseon Dynasty.

• Journal of the Korean Society for Heat Treatment
• /
• v.12 no.2
• /
• pp.129-135
• /
• 1999

The effects of Ag addition on the microstructures and mechanical properties of 7050 Al alloy were investigated. Various homogenizing and aging treatments were carried out to analyze the controversial effects of Ag in 7050 Al alloy. Transmission electron microscopy(TEM) was used for microstructural analysis. The hardening precipitates(${\eta}^{\prime}$) become finer with Ag addition. It suggests that Ag promotes easier nucleation of ${\eta}{\prime}$. The strength of overaged Ag bearing alloys are higher than that of Ag free alloy. Hardening precipitates(${\eta}^{\prime}$) in Ag bearing alloys are smaller than that of Ag free alloys, because the growth rate of ${\eta}^{\prime}$ during overaging stage is lower in Ag bearing alloys.

• Journal of the Korean Society for Heat Treatment
• /
• v.13 no.2
• /
• pp.103-107
• /
• 2000

Effect of aging treatment on the microstructures and mechanical properties of 7N01 Al alloy was investigated by differential scanning calorimetry, transmission electron microscopy, microhardness measurement and tensile test. Maximum hardness(125.7Hv) and tensile strength(447.3MPa) were obtained from the specimen aged at $120^{\circ}C$ for 32hrs. The major precipitation hardening phase was confirmed as coherent $MgZn_2({\eta}^{\prime})$ phase. Microhardness changes after peakaged condition showed very large decrease upon increased aging time. This result was attributed to the high transformation rate from coherent ${\eta}^{\prime}$ to incoherent ${\eta}$. It was found that the precipitation sequence of 7N01 Al alloy was GP zone${\rightarrow}$metastable spherical hcp $MgZn_2({\eta}^{\prime}){\rightarrow}$ equilibrium rodlike hcp $MgZn_2({\eta})$.