Tungsten carbide (WC) hard materials are used in various industries and possess a superior hardness compared to other hard materials. They have particularly high melting points, high strength, and abrasion resistance. Accordingly, tungsten carbide hard materials are used for wear-resistant tools, cutting tools, machining tools, and other tooling materials. In this study, the WC-5wt.%Co, Fe, Ni hard materials are densified using the horizontal ball milled WC-Co, WC-Fe, and WC-Ni powders by a spark plasma sintering process. The WC-5Co, WC-5Fe, and WC-5Ni hard materials are almost completely densified with a relative density of up to 99.6% after simultaneous application of a pressure of 60 MPa and an electric current for about 15 min without any significant change in the grain size. The average grain size of WC-5Co, WC-5Fe, and WC-5Ni that was produced through SPS was about 0.421, 0.779, and 0.429 μm, respectively. The hardness and fracture toughness of the dense WC-5Co, WC-5Fe, WC-5Ni hard materials were also investigated.

In this study, Fe-Cu-C alloy is sintered by spark plasma sintering (SPS). The sintering conditions are 60 MPa pressure with heating rates of 30, 60 and 9oC/min to determine the influence of heating rate on the mechanical and microstructure properties of the sintered alloys. The microstructure and mechanical properties of the sintered Fe-Cu-C alloy is investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The temperature of shrinkage displacement is changed at 450oC with heating rates 30, 60, and 90oC/min. The temperature of the shrinkage displacement is finished at 650oC when heating rate 30oC/min, at 700oC when heating rate 60oC/min and at 800oC when heating rate 90oC/min. For the sintered alloy at heating rates of 30, 60, and 90oC/min, the apparent porosity is calculated to be 3.7%, 5.2%, and 7.7%, respectively. The hardness of the sintered alloys is investigated using Rockwell hardness measurements. The objective of this study is to investigate the densification behavior, porosity, and mechanical properties of the sintered Fe-Cu-C alloys depending on the heating rate.

Cu-Mn compacts are fabricated by the pulsed current activated sintering method (PCAS) for sputtering target application. For fabricating the compacts, optimized sintering conditions such as the temperature, pulse ratio, pressure, and heating rate are controlled during the sintering process. The final sintering temperature and heating rate required to fabricate the target materials having high density are 700oC and 80oC/min, respectively. The heating directly progresses up to 700oC with a 3 min holding time. The sputtering target materials having high relative density of 100% are fabricated by employing a uniaxial pressure of 60 MPa and a sintering temperature of 700oC without any significant change in the grain size. Also, the shrinkage displacement of the Cu-Mn target materials considerably increases with an increase in the pressure at sintering temperatures up to 700oC.

The effect of carrier gases (He, ) on the properties of Ti coating layers were investigated to manufacture high-density Ti coating layers. Cold spray coating layers manufactured using He gas had denser and more homogenous structures than those using gas. The He gas coating layers showed porosity value of 0.02% and hardness value of Hv 229.1, indicating more excellent properties than the porosity and hardness of gas coating layers. Bond strengths were examined, and coating layers manufactured using He recorded a value of 74.3 MPa; those manufactured using gas had a value of 64.6 MPa. The aforementioned results were associated with the fact that, when coating layers were manufactured using He gas, the powder could be easily deposited because of its high particle impact velocity. When Ti coating layers were manufactured by the cold spray process, He carrier gas was more suitable than gas for manufacturing excellent coating layers.

Cold spray deposition using Titanium powder was carried out to investigate the effects of powder morphology and powder preheating on the coating properties such as porosity and hardness. The in-flight particle velocity of Ti powder in cold spray process was directly measured using the PIV (particle image velocimetry) equipment. Two types of powders (spherical and irregular ones) were used to manufacture cold sprayed coating layer. The results showed that the irregular morphology particle appeared higher in-flight particle velocity than that of the spherical one under the same process condition. The coating layer using irregular morphology powder represented lower porosity level and higher hardness. Two different preheating conditions (no preheating and preheating at ) were used in the process of cold spraying. The porosity decreased and the hardness increased by conducting preheating at . It was found that the coating properties using different preheating conditions were dependent not on the particle velocity but on the deformation temperature of particle. The deposition mechanism of particles in cold spray process was also discussed based on the experimental results of in flight-particle velocity.

This study investigated the effects of annealing environment for the densification and purification properties of pure titanium coating layer manufactured by cold spraying. The annealing was conducted at /1 h and three kinds of environments of vacuum, Ar gas, and mixture gas were controlled. Cold sprayed Ti coating layer (as sprayed) represented 6.7% of porosity and 228 HV of hardness, showing elongated particle shapes (severe plastic deformation) perpendicular to injection direction. Regardless of gas environments, all thermally heat treated coating layers consisted of pure -Ti and minimal oxide. Vacuum environment during heat treatment represented superior densification properties (3.8% porosity, 156.7 HV) to those of Ar gas (5.3%, 144.5 HV) and mixture gas (5.5%, 153.1 HV). From the results of phase analysis (XRD, EPMA, SEM, EDS), it was found that the vacuum environment during heat treatment could be effective for reducing oxide contents (purification) in the Ti coating layer. The characteristic of microstructural evolution with heat treatment was found to be different at three different gas environments. The controlling method for improving densification and purification in the cold sprayed Ti coating material was also discussed.

This study analyzes the resistance spot weldability of DP60 steels. To analyze the resistance spot weldability of DP60 steels, tensile strength test and macro-section test were conducted for the resistance spot welds. Acceptable welding conditions were determined as a function of the resistance spot welding process parameters such as electrode force, welding time, and welding current. The lower limit of the welding lobe was the minimum shear tension strength for 590MPa-grade steel while the upper limit was determined whether or not expulsion was detected.

This study attempted to manufacture a Cu-15 at.%Ga coating layer via the cold spray process and investigated the effect of heat treatment environment on the properties of cold sprayed coating material. Three kinds of heat treatment environments, +argon, pure argon, and vacuum were used in this study. Annealing treatments were conducted at /1 hr. With the cold sprayed coating layer, pure -Cu and small amounts of were detected in the XRD, EDS, EPMA analyses. Porosity significantly decreased and hardness also decreased with increasing annealing temperature. The inhomogeneous dendritic microstructure of cold sprayed coating material changed to the homogeneous and dense one (microstructural evolution) with annealing heat treatment. Oxides near the interface of particles could be reduced by heat treatment especially in vacuum and argon environments. Vacuum environment during heat treatment was suggested to be most effective one to improve the densification and purification properties of cold sprayed Cu-15 at.%Ga coating material.

In this study, Ti powders were fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH) method.The Ti powders were prepared from the spark plasma sintering (SPS) and their microstructure was investigated.Hydrogenation reactions of Ti scrap occurred at near 450oC with a sudden increase in the reaction temperature and thedecreasing pressure of hydrogen gas during the hydrogenation process in the furnace. The dehydrogenation process was alsocarried out at 750oC for 2 hrs in a vacuum of 10-4torr. After the HDH process, deoxidation treatment was carried out withthe Ca (purity: 99.5%) at 700oC for 2 hrs in the vacuum system. It was found that the oxidation content of Ti powder thatwas deoxidized with Ca showed noticeably lower values, compared to the content obtained by the HDH process. In orderto fabricate the Ti compacts, Ti powder was sintered under an applied uniaxial punch pressure of 40 MPa in the range of900-1200oC for 5 min under a vacuum of 10-4torr. The relative density of the compact was 99.5% at 1100oC and the tensilestrength decreased with increasing sintering temperature. After sintering, all of the Ti compacts showed brittle fracturebehavior, which occurred in an elastic range with short plastic yielding up to a peak stress. Ti improved the corrosionresistance of the Ti compacts, and the Pd powders were mixed with the HDH Ti powders.

In this study, Ti powder was fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH)method. Hydrogenation reactions of Ti scrap occurred at near 450oC with a sudden increase in the reactiontemperature and the decreasing pressure of hydrogen gas during the hydrogenation process in the furnace. Thedehydrogenation process was also carried out at 750oC for 2hrs in a vacuum of 10-4torr. After the HDHprocess, a deoxidation treatment was carried out with the Ca(purity: 99.5) at 700oC for 2hrs in the vacuumsystem. It was found that the oxidation content of Ti powder that was deoxidized with Ca showed noticeablylower values, compared to the content obtained by HDH process. In order to fabricate Ti compacts, Ti powderwas sintered at 1100~1400oC for 2hrs under a vacuum of 10-4torr. The relative density of compact was 94.9%at 1300oC. After sintering, all of the Ti compacts showed brittle fracture behavior, which occurred in an elasticrange with short plastic yielding up to a peak stress.

In this study, Ti powder was fabricated from Ti scrap by a hydrogenation-dehydrogenation (HDH)method. The Ti powders were compacted by Spark plasma sintering (SPS) and the microstructure andmechanical properties of the powders were investigated. A hydrogenation reaction of Ti scrap occurred attemperatures near 450oC with a sudden increase in the reaction temperature and a decrease in the pressureof the hydrogen gas as measured in a furnace during the hydrogenation process. In addition, a dehydrogenationprocess was carried out at 750oC for 2hrs in a vacuum of 10-4torr. The Ti powder sizes obtained byhydrogenation-dehydrogenation and mechanical milling processes were in the range of 1~90µm and 1~100µm,respectively. To fabricate Ti compacts, Ti powders were sintered under an applied uniaxial punch pressure of40 MPa at in a range of 900~1200oC for 5 min. The relative density of a SPSed compact was 99.6% at 1100oC,and the tensile strength decreased with an increase in the sintering temperature. However, the hardnessincreased as the sintering temperature increased.

SOFC (Solid Oxide Fuel Cell) Ni-YSZ anode was fabricated by the spark plasma sintering (SPS) process and its microstructure and electrical properties were investigated in this study. The spark plasma sintering process was carried out at for holding time of 5 min under 40 MPa. To fabricate Ni-YSZ anode, the SPS processed specimens were reduced at under atmosphere. The reduced specimens showed relative density of according to sintering temperature. And also, the electrical conductivity of reduced specimens after sintering at 900 and showed (S/cm) values at the measuring range of .

Microstructure and mechanical properties of WC-3wt% Co cemented carbides, fabricated by a sparkplasma sintering (SPS) process, were investigated in this study. The WC-3wt%Co powders were sintered at900~1100oC for 5min under 40MPa in high vacuum. The density and hardness were increased as the sinteringtemperature increased. WC-3wt%Co compacts with a relative density of 97.1% were successfully fabricated at1100oC. The fracture toughness and hardness of a compact sintered at 1100oC were 21.6MPa·m1/2 and4279Hv, respectively.

In this study, tantalum (Ta) compacts were fabricated in a spark plasma sintering (SPS) process and their microstructure and mechanical properties were investigated. Ta compacts with a density of 99% were successfully fabricated by controlling the sintering conditions of the current and the temperature. The density and hardness were increased as the sintering temperature increased. The Ta2C compound was observed at the surface of the compacts due to the contact between the Ta powder and graphite mold during the sintering process. The main fracture mode showed a mixed type with intergranular and transgranular modes having some roughness.