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Stainless steel-based composites (SMCs) mixed with 316L stainless steel powder and Fe-Cr-B based M alloys powder ed M) powder were manufactured using the powder injection molding (PIM) process, and their microstructure and mechanical properties were investigated. To examine the effect of M content on the properties of SMCs, the M fraction was controlled to 30 vol.%, 50 vol.%, and 70 vol.%. It was observed that PIM-processed Fe-Cr-B/316L SMCs (30 vol.%, 50 vol.%, 70 vol.%) had γ-austenite and minor α-ferrite as a matrix, and (Cr, Fe)2B was formed as a reinforced phase. In tensile tests at room temperature, the yield strengths of the 30 vol.%, 50 vol.%, 70 vol.% M SMCs were measured to be 519.9 MPa, 574.1 MPa, and 604.8 MPa (peak stress), respectively. From the fracture surface observation results, it was found that the deformation behavior changed from the intergranular fracture of boride to intergranular fracture between the matrix and boride, as the M fraction increased. Based on the above results, the deformation and fracture mechanisms of novel Fe-Cr-B/316L SMCs are also discussed.

This study investigated the effect of the electromagnetic stirring (EMS) process on the microstructure and mechanical properties of hyper-eutectic Al-15 wt.%Si alloy. The tensile and high-cycle fatigue properties of the EMS Al-15wt.%Si alloy were examined and compared with conventional direct chill (DC) cast alloy. The initial microstructure of the as-cast DC alloy showed a coarse primary Si of 70 µm, in contrast to the size (40 µm) of the as-cast EMS alloy. The DC extruded alloy exhibited a massive primary Si size of 40~55 µm. In contrast, the EMS extruded alloy had a spherical primary Si with 30~40 µm sizes. The average grain sizes were measured to be 8.8 µm (EMS extruded alloy) and 11.4 µm (DC extruded alloy), respectively. The EMS process was confirmed to contribute to the refinement of the grain size and the primary Si size of the hyper-eutectic Al-Si alloy. The yield strengths at room temperature were measured to be 388.0 MPa (EMS extruded alloy) and 375.0 MPa (DC extruded alloy), and the tensile strengths were 426.0 MPa (EMS extruded alloy) and 412.4MPa (DC extruded alloy), respectively. The elongations of both alloys were similar at room temperature. The fatigue limit of the EMS extruded alloy (130 MPa) was higher than that of the DC extruded alloy (120 MPa). The EMS extruded alloy exhibited superior fatigue resistance compared to the DC extruded alloy, regardless of the cyclic stress condition. This study also discussed the potential value of the EMS process as a method for improving the properties of hyper-eutectic Al-Si alloy, as well as the deformation and fracture mechanisms of the EMS Al-15wt.%Si alloy.

The effect of tailored microstructures in 0.5 wt% CaO added AZ31 on tensile, high-cycle fatigue, and fatigue crack growth properties was examined. By adding CaO, the average grain size (AGS) was significantly reduced from 4.25±2.32 μm (conventional AZ31) to 2.42±1.60 μm (CaO-AZ31). The fineprecipitates of CaO-AZ31 were more evenly distributed and their fraction was higher than those of conventional AZ31. The fine-precipitates were identified as Al8Mn4Ca and (Mg, Al)2Ca in CaO-AZ31, meanwhile, were identified as Al8Mn5 and Mg17Al11 in conventional AZ31. The tensile test results showed that the yield strengths of CaO-AZ31 and conventional AZ31 were 238.0 MPa and 206.7 MPa, respectively. The elongation-to-failure also increased when CaO was added. The improved tensile properties of CaO-AZ31 could be explained by grain refinement and precipitation hardening. The high-cycle fatigue limit also increased about 15% with added CaO. The fatigue limits as a function of the tensile strengths of CaO-AZ31 and conventional AZ31 were 0.508 and 0.457, respectively. The origin of the improved fatigue resistance was attributed to inhibition of the formation of DTs, which acted as the fatigue crack source, in CaO-AZ31. In contrast, the fatigue crack growth property did not change when CaO was added. Based on the above findings, the relationships between microstructure, mechanical properties and deformation mechanisms are also discussed.

In this study, high-strength pure Cu bulk material was manufactured using a cold spray additive manufacturing process, and its microstructure, tensile and compressive deformation behaviors were investigated and compared. The cold spray additive manufactured Cu bulk material showed a heterogeneous grain structure consisting of fine-grains and coarse-grains, and only α – Cu single phase was identified. The cold spray Cu exhibited yield strengths of ~415 MPa in tensile- and compression tests, indicating that it had similar mechanical properties in different deformation modes. The yield strength values were similar to that of Cu manufactured by equal channel angular pressing (ECAP), a severe plastic deformation (SPD) method which enables ultra-high strength. Concerning tensile characteristics, the cold sprayed Cu exhibited partial plastic deformation that has not been reported to date. In addition, some nano-sized dimples, suggesting metallurgical bonding, were also found in the fracture surface. Regarding compression characteristics, the strain softening phenomenon, which is not a general tendency in room temperature deformation, appeared. This unique softening behavior was attributed to dynamic recovery and dynamic recrystallization during compression testing. Based on the above results, we discuss the tensile/compressive deformation behavior of the cold spray Cu bulk material, and predict compressive deformation behavior considering the constitutive equation.

Polycrystalline diamond compact (PDC) has excellent wear resistance, high impact resistance, superior fatigue properties, and has been used in the oil and gas drilling industries. This study investigated the effect of Co leaching on the microstructure, vertical turning lathe (VTL) wear properties of PDCs manufactured by high-temperature and high-pressure (HTHP) sintering. The VTL wear test has the advantage of simulating the actual oil drilling environment by using granite as the workpiece. PDC sintered material that did not receive Co leaching was named HTHP sintered PDC-A, and the material subjected to Co leaching was called Co-leached PDC-B in this study. As a result of XRD analysis of both PDCs, diamond and WC peaks were detected, and only the HTHP sintered PDC-A exhibited some Co peaks. In the HTHP sintered PDC-A, the binder WC and Co were evenly distributed at the diamond interface. However, in the Co-leached PDC-B, some empty spaces were observed at the diamond interface. The HTHP sintered PDCA exhibited a similar or slightly higher VTL wear resistance than the Co-leached PDC-B, but only in the short sliding distance. In the long sliding distance after 9 km, Co-leached PDC-B showed significantly superior wear resistance compared to the HTHP sintered PDC-A. The HTHP sintered PDC-A exhibited both abrasive and adhesive wear behaviors, while the Co-leached PDC-B showed only abrasive wear. Based on the above results, the VTL wear mechanism of PDCs, and ways of improving wear resistance were also discussed.

The powder-alloyed metallic sheet foam manufacturing process has the advantage of being able to control pore shape, size, and distribution more easily and homogeneously than conventional foam manufacturing processes. The effects of strain rate and tensile direction on the mechanical properties of Ni-Cr-Al superalloy foam fabricated by powder alloying method were investigated. As a result of structural characteristics obtained by X-ray tomography and scanning electron microscopy, average pore sizes were measured to be 2762.4 μm (normal direction), 2709.1 μm (rolling direction, RD), and 2518.4 μm (transverse direction, TD) respectively. The γ-Ni matrix and γ’-Ni3Al (which was evenly distributed in the strut) were identified as the main constituent phases of the Ni-Cr-Al foam used in this study. Tensile tests were conducted with strain rates of 10−2 ~ 10−4 s−1 along the rolling and transverse directions. The results showed that the tensile strength in the RD direction was 1.84~2.01 MPa, and in the TD direction was 1.2~1.27 MPa. The elongation in the TD direction was higher (30~36%) than in the RD direction (17~22%). It is noteworthy that the effect of quasi-static strain rate on the tensile strength and elongation was negligible. However, the loading direction was found to change mechanical properties significantly. This study also discussed the deformation behavior of the Ni-Cr-Al superalloy foam through observations of the fracture surface, and realtime observations during tensile tests in different directions.

Al 3003 alloy was manufactured by strip casting process, and the effect of post heat-treatment on tensile and fatigue properties was investigated. The strip cast Al 300 alloy exhibited a unique globular shaped rapid-cooled solidification structure, and the microstructural characteristic remained after heat-treatment. Asstrip cast (F) and heat-treated (O) alloys were commonly composed of Al matrix and strengthening phases such as Al6(Mn,Fe), α-Al(Mn,Fe)Si. In the phase analysis and Factsage simulation result, Al6(Mn,Fe) fraction increased while α-Al(Mn,Fe)Si fraction decreased after heat-treatment. Strengthening phases were more uniformly and finely distributed in the case of O alloy, than F alloy. In the Vickers hardness results, F alloy (measured 59.7 Hv) showed higher hardness than O alloy (measured 53.4 Hv). The yield strengths (YS) and ultimate tensile strengths (UTS) measured 124.8 MPa and 166.4 MPa (F alloy), and 111.2 MPa and 167.2 MPa (O alloy), respectively. F alloy exhibited superior YS compared to O alloy, while UTSs were similar in both alloys. For elongation, the F alloy (19.6%) had a lower value than the O alloy (23.0%). High cycle fatigue tests were performed at room temperature under a stress ratio (R) of 0.1 and frequency (F) of 10 Hz. The F alloy exhibited higher fatigue than the O alloy under all cyclic stress conditions. However, the deviation in the fatigue property of the F alloy was relatively broader than the O alloy. Tensile and fatigue fracture surfaces were examined, and the tensile and fatigue deformation mechanisms of the strip cast Al 3003 alloy were also discussed.

A block Ni-Cr-Al superalloy foam with dimensions of 300 mm (width direction, WD) × 500 mm (rolling direction, RD) × 60 mm (normal direction, ND) was fabricated using powder alloying, multi-sheet stacking, and hot rolling processes. The structural characteristics, microstructure, and mechanical asymmetry of the block Ni-based foam were investigated. Analysis of the structural features showed that the interfaces between the sheets had complex strut interactions, such as contacted (deformed) and intersected struts. The average pore size along the directions was measured to be 2569.6 μm (WD), 2988.1 μm (RD), and 2493.2 μm (ND). The average thickness of the strut was 340.8 μm, and the wall thickness of the strut was 27.7 μm. The elemental distributions in the struts were uniformly controlled, and the block foam consisted of γ (matrix) and γ ' (Ni3Al) phases. Tensile properties in the ND direction showed a yield strength of 0.175 MPa, tensile strength of 0.233 MPa, and elongation of 2.54%, while the tensile properties in the RD direction were 1.27 MPa (YS), 3.01 MPa (UTS), 8.92% (El.) respectively. The foam was observed to have a compressive yield strength of 0.795 MPa in the ND direction, and that of 2.18 MPa in the RD direction were obtained. The asymmetry and anisotropy of these mechanical properties could be explained by the difference in pore sizes along the direction, and the structural characteristics of the sheet interface generated by sheet stacking and rolling.

We fabricated the IN 713C alloy by a metal injection molding (MIM) process and investigated the high temperature tensile properties. The microstructure of the MIMed IN 713C alloy mainly consisted of γ, γ′ and carbides. 0.98% (area fraction) of the pores was observed near the surface of the specimen, whereas 0.27% of the pores were located in the interior of the specimens. Tensile tests were conducted from room temperature to 900 °C. The result of the tensile tests showed that this alloy had similar or somewhat higher strengths (YS: 734 MPa, UTS: 968 MPa, elongation: 7.16% at room temperature) from RT to 700 °C than those of cast IN 713C alloys. Above 700 °C, however, strengths decreased rapidly with an increasing temperature (lower than those of cast IN 713C). The observation results of fractography revealed that the tensile fracture of the MIMed IN 713C alloy started near the surface defects and then the initial crack propagated along the inter-particle region where oxides were observed regardless of deformation temperatures. †(Received Jully 11, 2013)