An irradiation hardening of Inconel 718 produced by selective laser melting (SLM) was studied based on the microstructural observation and mechanical behavior. Ion irradiation for emulating neutron irradiation has been proposed owing to advantages such as low radiation emission and short experimental periods. To prevent softening caused by the dissolution of ' and '' precipitates due to irradiation, only solution annealing (SA) was performed. SLM SA Inconel 718 specimen was ion irradiated to demonstrate the difference in microstructure and mechanical properties between the irradiated and non-irradiated specimens. After exposing specimens to Fe3+ ions irradiation up to 100 dpa (displacement per atom) at an ambient temperature, the hardness of irradiated specimens was measured by nanoindentation as a function of depth. The depth distribution profile of Fe3+ and dpa were calculated by the Monte Carlo SRIM (Stopping and Range of Ions in Matter)-2013 code under the assumption of the displacement threshold energy of 40 eV. A transmission electron microscope was utilized to observe the formation of irradiation defects such as dislocation loops. This study reveals that the Frank partial dislocation loops induce irradiation hardening of SLM SA Inconel 718 specimens.

Alloys of nylon(PA6) and ethylene-propylene-diene polymer, modified with maleic anhydride(MEPDM) were prepared using a melt kneading process. This study focuses on the effects of the content of MEPDM in PA6 blend on the mechanical and thermal properties of such blends where MEPDM is the dispersed phase. Mechanical properties were examined by stress-strain measurements and impact strength test. Both impact strength of PA6/MEPDM at room temperature and at -20℃ were improved up to 400-550% with the amounts of MEPDM. However, PA6/MEPDM containing 3-5 wt% of MEPDM showed the about 700kgf/m2 of the maximum tensile strength but 8.5 % of the lowest elongation. For certain compositions of PA6 with rubbery MEPDM, the interesting reduction of elongation is caused by the reaction of the polyamide amine end groups with maleic anhydride portion in MEPDM, that provided a reinforcement in the PA6 matrix. In addition, the introduction of antistatic agent on the surface of alloys causes significant reduction of their surface electrostatic resistance.

Energy resistance welding (ERW) is a pipe-producing process that has high productivity and low manufacturing cost. However, the high heat input of ERW degrades the mechanical property of the pipe. This study investigates the effect of heat input and alloying elements on microstructure and mechanical properties of ERW pipes. As the heat input increased, the ferrite amount increased. The ferrite amount in the weld centerline was larger than t at in the weld boundary. Medium carbon steels (S45C and K55) having 0.3~0.4wt.% carbon yielded a significant difference of ferrite amount in the weld centerline and weld boundary. High alloyed steels (DP780 and K55) having 1.5~1.6wt.% Mn showed a ferrite rich zone in the weld centerline. These phenomena are probably due to decarburization and demanganisation in the weld centerline. As the ferrite fraction increased, the hardness decreased a little for the S45C steels. In addition, DP780 steels and K55 steels showed that the hardness drops when those steels have a ferrite rich zone. But we demonstrated the good tensile property of the DP780 steels and K55 steels in which Mn is included.

High-energy mechanical milling (HEMM) and sintering into Al-Mg alloy melt were employed tofabricate an Al alloy matrix composite reinforced with submicron and micron sized Al2O3 particles. Al-basedmetal matrix composite (MMC) reinforced with submicron and micron sized Al2O3 particles was successfullyfabricated by sintering at 1000oC for 2h into Al-Mg alloy melt, which used high energy mechanical milled Al-SiO2-CuO-ZnO composite powders. Submicron/micron-sized Al2O3 particles and eutectic Si were formed by in situdisplacement reaction between Al, SiO2, CuO, and ZnO during sintering for 2h into Al-Mg alloy melt and werehomogeneously distributed in the Al-Si-(Zn, Cu) matrix. The refined grains and homogeneously distributedsubmicron/micron-sized Al2O3 particles had good interfacial adhesive, which gives good wear resistance withhigher hardness.

In this study, the bottom-up powder metallurgy and the top-down severe plastic deformation (SPD) techniques for manufacturing bulk nanomaterials were combined in order to achieve both full density and grain refinement without grain growth of rapidly solidified Al-20 wt% Si alloy powders during consolidation processing. Continuous equal channel multi-angular processing (C-ECMAP) was proposed to improve low productivity of conventional ECAP, one of the most promising method in SPD. As a powder consolidation method, C-ECMAP was employed. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructures of the ECMAP processed materials. It was found that effective properties of high strength and full density maintaining nanoscale microstructure are achieved. The proposed SPD processing of powder materials can be a good method to achieve fully density and nanostructured materials.

Two atomized alloy powders were pre-compacted by cold and subsequently hot forged at temperatures ranging from 653K to 845K. The addition of Cu and Mg causes a decrease in the eutectic reaction temperature of Al-10Si-5Fe-1Zr alloy from 841K to 786K and results in a decrease of flow stress at the given forging temperature. TEM observation revealed that in addition to Al-Fe based intermetallics, Al2Cu and Al2CuMg intermetallics appeared. The volume fraction of intermetallic dispersoids increased by the addition of Cu and Mg. Compressive strength of the present alloys was closely related to the volume fraction of intermetallic dispersoids.

The alumina dispersion-strengthened (DS) C15715 Cu alloy fabricated by a powder metallurgy route was annealed at temperatures ranging from in the air and in vacuum. The effect of the annealing on microstructural stability and room-temperature mechanical properties of the alloy was investigated. The microstructure of the cold rolled OS alloy remained stable until the annealing at in the air and in vacuum. No recrystallization of original grains occurred, but the dislocation density decreased and newly formed subgrains were observed. The alloy annealed at in the air experienced recrystallization and grain growth took place, however annealing in vacuum at did not cause the microstructural change. The mechanical property of the alloy was changed slightly with the annealing if the microstructure remained stable. However, the strength of the specimen that was recrystallized decreased drastically.

Copper-10 wt. % tungsten alloyed powder was obtained by co-reduction of mixed tungsten-trioxide and copper oxide powders at 973 K for 7.2 Ks. In the alloy obtained by pressure-assisted sintering of this co-reduced powder, ultra fine tungsten particles (about 100nm) were dispersed uniformly in the copper matrix. At room temperature, the hardness of this alloy was Hv151 and the electrical conductivity was 85% IACS. After annealing at 1173 K for 3.6 Ks, the hardness and electrical conductivity were Hv147 and 84% IACS, respectively, and were same as before annealing. It was confirmed that the hardness and electrical conductivity of this alloy were hardly influenced by annealing condition since the microstructure of this alloy is highly stabilized.

A study on the improvement of the impact energy in 93W heavy alloy with a Ni/Fe ratio of 9/1 has been carried out as a function of heat treatment temperature. The obtained results were compared to that of the traditional alloy system in which the Ni/Fe ratio is 7/3 or 8/2. With increasing heat treatment temperature from 1150 to 125, the impact energy of the alloy with the Ni/Fe ratio of 9/1 is remarkably increased from 42 to 72 J, which is higher than that of traditional alloy, up to 118 and then saturated. Fracture mode was also changed from brittle W/W boundary failure to W cleavage. The temperature showing the dramatic shrinkage by dilatometric anaysis of the heavy alloy with Ni/Fe ratio of 9/1 was found to be 1483 , which is higher than that (146) of the heavy alloy with Ni/Fe ratio of 7/3. Auger Electron Spectroscopy showed that the segregation of impurities, such as S, P, and C in W/W grain boundary was considerably decreased with increasing heat treatment temperature from 1150 to l18. From the above results, it was found that the impurity segregation in W/W grain boundary played an important role on the decrease of impact properties, and the heat treatment temperature should be appropriately chosen, as considering the Ni/Fe ratio of the alloy, in order to get good impact properties.

AI-2.5wt%Li 합금을 시효처리하여 시효거동과 인장성질에 미치는 δ' 상의 영향을 조사하였다. δ' 상의 입자 반경은 시효 시간의 1/3승에 비례하여 조대화하였다. δ' 상과 기지상과의 계면에너지는 0.0073 J/m2, 확산계수는 1.42cm2/sec, 초대화 거동은 MLSW이론에 부합됨을 알 수 있었다. 미세하고 균일하게 분포한 δ'상은 전반적으로 인장강도의 상승을 가져왔으며, 평형상인 δ상의 석출과 이로 인한 무석출물대의 존재로 과시효시 강도가 감소하였다. 인장변형시 전위는 초전위로 아시효와 피크시효시에는 δ'상을 전단하지만 과시효시에는 δ'상을 전단하지 못하고 우회하여 전위루우프를 형성한다.

dynamic strain gage와 12bit AD(analog to digital converter)를 이용한 새로운 제진특성 측정 장치를 제작하였다. 이 장치를 이용하여 일반재료와 고제진재료의 제진특성을 연구하였다. 또한 열처리 조건, 초기 진동 진폭, 그리고 내부응력의 변화에 따른 SDC(specific damping capacity)변화에 관하여 연구하였다. 일반재료와 제진재료의 비교에서, 제진재료는 진동을 가한 후 0.4초 이내에 진동 진폭이 거의 사라졌지만, 같은 시간에 일반재료의 진동 진폭은 거의 감소하지 않았다. Fe-16wt. %Cr계 합금의 제진 특성은 노냉일 때 SDC max 가 40%이상이었고, Fe-5.5wt.%Ai합금의 제진 특성은 공냉일 때 SDC max값이 30%이상이었다. 초기 진동 진폭이 증가할수록 최대 제진 특성치는 낮은 진동 진폭 영역으로 이동하였다. 제진 특성은 내부 응력이 증가할수록 급격한 감소를 보였으며, 본 연구에서 개발한 제진측정 장치는 낮은 진동 진폭의 영역에서 정확한 제진 특성 측정이 가능하였다.