In this study, tensile properties of TiC reinforced SKD11 tool steel matrix composites were investigated with different heat-treatment conditions and volume fractions of reinforcement. TiC is well-known for reinforcement in Fe-matrix because of its high melting point, low density and elastic modulus...
In this study, tensile properties of TiC reinforced SKD11 tool steel matrix composites were investigated with different heat-treatment conditions and volume fractions of reinforcement. TiC is well-known for reinforcement in Fe-matrix because of its high melting point, low density and elastic modulus and especially exhibits good melt wettability with iron and steel matrices. Generally, TiC-Fe composites have been produced by powder metallurgy, but there are some problems such as a high cost, mechanical properties and a limitation of enlargement. In order to overcome these problems, TiC-SKD11 composite manufactured by infiltration having high volume fraction of TiC, could have cost-effectiveness and feasibility of enlargement, as compared to that of powder metallurgy. TiC reinforced SKD11 matrix composites fabricated by powder metallurgy and infiltration have high volume fraction of TiC particles(43%, 53%, 64%). Especially, TiC-SKD11 composite fabricated by infiltration showed a homogeneous distribution of TiC within the matrix. The complete infiltration of the molten steel was confirmed from the microstructure showing that the penetration of the liquid metal reached geometrically complex regions without any interfacial flaws. The results about atomic arrays obtained from HRTEM show that TiC and steel atoms are connected through semi-coherent nature, i. g. . Tensile tests were conducted at 25, 700, 750 and 800 ℃. The composite exhibited the enhanced strength compared with the unreinforced SKD11 and its reinforcement was most effective at 800 oC. After tensile test, fracture behaviors of the TiC-SKD11 composite were investigated using SEM (scanning electron microscope) by investigating microstructures below fractured surface. At 25 and 700 oC, cracks almost initiated at Cr-rich M7C3 carbide and then propagated through adjacent TiC. A significant amount of transgranular TiC cracking was found along the {100} cleavage plane, which was responsible for main fracture of the composite. However, at and above 750 oC debonding of TiC interface began to be operative, which imply that transition temperature from TiC cleavage fracture to interfacial decohesion may be present around 750 oC. In order to investigate the effect of reinforcement volume fraction, tensile properties of the TiC-SKD11 composites having 43%, 53%, 64% volume fraction of TiC were obtained at 25 and 700 ℃. The degree of strengthening effect of the composite became significant when volume fraction of reinforcement decreased at 25 ℃, but increased at 700 ℃. In addition, in order to determine the effect of heat-treatment, tensile properties of variously heat-treated (as-infiltrated, softening, hardening, hardening followed by 300 ℃ or 500 ℃ tempering) composites having 64% volume fraction of TiC were compared from each other at 25 and 700 oC. At 25 oC, softening heat-treated composite having relatively soft matrix shows the highest degree of strengthening. On the contrary, regardless of the heat-treatment condition, the composites have similar tensile properties 700 oC because the matrices of the composites can be changed to 700 oC tempered structure. Additionally, the strengthening mechanisms of the infiltrated composite were discussed in terms of a dislocation, residual stress, load transfer from steel to TiC reinforcement. Finite element simulation was conducted to predict quantitatively the stress concentration at the interface between TiC and steel matrix using ANSYS.
In this study, tensile properties of TiC reinforced SKD11 tool steel matrix composites were investigated with different heat-treatment conditions and volume fractions of reinforcement. TiC is well-known for reinforcement in Fe-matrix because of its high melting point, low density and elastic modulus and especially exhibits good melt wettability with iron and steel matrices. Generally, TiC-Fe composites have been produced by powder metallurgy, but there are some problems such as a high cost, mechanical properties and a limitation of enlargement. In order to overcome these problems, TiC-SKD11 composite manufactured by infiltration having high volume fraction of TiC, could have cost-effectiveness and feasibility of enlargement, as compared to that of powder metallurgy. TiC reinforced SKD11 matrix composites fabricated by powder metallurgy and infiltration have high volume fraction of TiC particles(43%, 53%, 64%). Especially, TiC-SKD11 composite fabricated by infiltration showed a homogeneous distribution of TiC within the matrix. The complete infiltration of the molten steel was confirmed from the microstructure showing that the penetration of the liquid metal reached geometrically complex regions without any interfacial flaws. The results about atomic arrays obtained from HRTEM show that TiC and steel atoms are connected through semi-coherent nature, i. g. . Tensile tests were conducted at 25, 700, 750 and 800 ℃. The composite exhibited the enhanced strength compared with the unreinforced SKD11 and its reinforcement was most effective at 800 oC. After tensile test, fracture behaviors of the TiC-SKD11 composite were investigated using SEM (scanning electron microscope) by investigating microstructures below fractured surface. At 25 and 700 oC, cracks almost initiated at Cr-rich M7C3 carbide and then propagated through adjacent TiC. A significant amount of transgranular TiC cracking was found along the {100} cleavage plane, which was responsible for main fracture of the composite. However, at and above 750 oC debonding of TiC interface began to be operative, which imply that transition temperature from TiC cleavage fracture to interfacial decohesion may be present around 750 oC. In order to investigate the effect of reinforcement volume fraction, tensile properties of the TiC-SKD11 composites having 43%, 53%, 64% volume fraction of TiC were obtained at 25 and 700 ℃. The degree of strengthening effect of the composite became significant when volume fraction of reinforcement decreased at 25 ℃, but increased at 700 ℃. In addition, in order to determine the effect of heat-treatment, tensile properties of variously heat-treated (as-infiltrated, softening, hardening, hardening followed by 300 ℃ or 500 ℃ tempering) composites having 64% volume fraction of TiC were compared from each other at 25 and 700 oC. At 25 oC, softening heat-treated composite having relatively soft matrix shows the highest degree of strengthening. On the contrary, regardless of the heat-treatment condition, the composites have similar tensile properties 700 oC because the matrices of the composites can be changed to 700 oC tempered structure. Additionally, the strengthening mechanisms of the infiltrated composite were discussed in terms of a dislocation, residual stress, load transfer from steel to TiC reinforcement. Finite element simulation was conducted to predict quantitatively the stress concentration at the interface between TiC and steel matrix using ANSYS.
주제어
#Composite Infiltration Transmission electron microscope (TEM) Interface Fracture behavior Strengthening mechanism Finite element simulation
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