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Two chromium-rich carbide hard-faced plates, alloy—A and alloy—B, were subjected to a 3-body dry sand abrasion test. The difference was in the coating microstructure. Alloy-A contains globular chromium carbide (M7C3 type) in the austenite matrix, whereas alloy—B is composed of a banded structure with an alternate layer of carbide and austenite. Alloy B showed a superior abrasion resistance (nearly 40%) than alloy—A. A detailed microstructural investigation was made on the abraded surface. The higher abrasive wear resistance of alloy-B was attributed to the coating morphology, the composite-like microstructure resulted in an effective strain distribution among the austenite matrix and carbides. This postulate was supplemented by higher average misorientation, which was observed at sub-surface regions of the worn-out specimen, leading to form a strain-induced martensite. However, in alloy—A, the abraded surface contained abundant broken carbides. [ABSTRACT FROM AUTHOR]

The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT.

In this paper, real-time cooling rate of Fe-Ti-C Metal Matrix Composites (MMCs) made by Direct Metal Deposition (DMD) are measured to monitor microstructure and carbide morphology. This research proves that carbide morphology developed by DMD of Fe–TiC composite coating on AISI 1020 carbon steel is highly affected by cooling rate and pre-heat. For this purpose, the DMD process is monitored by a thermal camera to obtain real-time values of the cooling rate resulted from a range of selected scan speeds. Two approaches are studied for the single-track depositions: (a) single speed and (b) dual speeds in which the scan speed changes during the deposition. The dual speed generates different preheat values during deposition and thus deviates the cooling rate. Consequently, the effect of cooling rate and preheat temperature are studied on carbide morphologies. Results show that scan speed plays the main role in the formation and distribution of TiC particles in the deposited layer by affecting the cooling rate and dilution (melt pool composition). Based on this research, it is possible to control the cooling rate in order to achieve specific carbide morphologies in the deposited layer. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) are used to characterize the deposited layers' microstructure. [ABSTRACT FROM AUTHOR]

The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT. [ABSTRACT FROM AUTHOR]

The influence of solution temperature on the microstructure evolution and creep behavior of a new Ni–Co base superalloy for turbine discs, including the grain morphology, grain boundary character distribution (GBCD), and grain boundary (GB) carbide morphology, was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results showed that the creep fracture life first increased and then decreased with increasing solution temperature. The alloy solution treated at 1140 °C exhibited the best creep properties, with a creep life of 209 h. The enhanced creep performance of this alloy can be explained as follows: the volume fraction of GB carbides increased with increasing solution temperature, the diffuse fine granular carbides relieved stress concentration and strengthened GBs, the coarse primary γ′ phases rapidly dissolved, and the volume fraction of the fine and dispersed secondary and tertiary γʹ phases significantly increased. The narrower channels in the γ matrix increased the resistance to dislocation motion. The coherent Σ3 twin boundaries (TBs) with low interface energy hindered the dislocations and stacking faults intersecting the TBs on different slip planes. The relative frequency of Σ3 TBs increased to 53.6% when the solution temperature was increased to 1140 °C. The high proportion of Σ3 TBs played a key role in improving the creep resistance of the alloy. • Microstructure and creep behaviors were studied at different solution temperatures. • Creep life increased at first and thereafter decreased as solution temperature increased. • The continuous rod-like morphology of the M 23 C 6 carbide degraded the creep properties. • The improved creep properties were determined by the increase of Σ3 TBs and fine γ′. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of Fe–TiC metal matrix composite during metal deposition with laser and arc welding techniques is of technical and economic interest for hard surfacing of engineering components. Recent studies linked the resistance to abrasive wear with the size and morphology of TiC precipitates, which are strongly dependent on the deposition conditions and, more importantly, on the alloy chemistry. In this study, the effect of silicon and manganese on the TiC precipitates was explored and different processing conditions were assessed. The characterisation included optical and scanning electron microscopy, X-ray diffraction and microhardness testing. The results indicate that silicon and manganese can have a significant effect on TiC size and morphology. Therefore, the composition of the matrix alloy offers an effective pathway to modify the microstructure of in-situ precipitated Fe–TiC metal matrix composites. [Copyright &y& Elsevier]