Correlation between surface damage and mechanical properties at micro- and nanometric length scale for WC-Co hardmetals

Cemented carbides (WC-Co) are ceramic-metal composite materials made by hard tungsten carbide particles bonded through a metallic binder matrix, mainly of cobalt. It is a hard material characterized by an exceptional combination of strength, toughness and wear resistance. As result, cemented carbides are first choice materials for cutting tools and wear parts. However, final shaping of these components usually require diamond grinding. During this hard machining, surface integrity may became altered, particulary in terms of compression stresses and/or microcracking. Such defects can locally affect the mechanical properties. The aim of this investigation is to analyze the influence of the surface finish quality on the mechanical properties at the surface level for WC-Co materials as well as the influence over the properties of a TiN coating deposited on hardmetal substrates. The study has been done at micrometric (to analyze the general properties) and nanometric scale (local properties aiming to capture residual stress state effects) by using nanoindentation and nanoscratch testing. Tests done in plain view prove that roughness plays an important role in the assessment of mechanical properties at the surface, as it induces significant scatter, as compared to results determined on cross-sections. Finally, a sequential polishing process has been done in order to extract the polishing rate for cemented materials as well as study how roughness affects the mechanical properties measured. This process points out that roughness can mask surface damage, like cracks or chipping, among others. As a final conclusion, an optimized protocol is proposed to study the mechanical properties of the samples with high roughness and exhibiting a compressive residual stress state

In-situ approach for thermal energy storage and thermoelectricity generation on the Moon: Modelling and simulation

Human, tele-operated rovers, and surface infrastructures are now being actively considered for lunar polar exploration. Current approaches to energy provision consider, among others, hybrid direct energy/chemical technologies, such as solar photovoltaic arrays, batteries, and regenerative fuel cells. Due to the long period of darkness on the Moon and the challenges this poses to the aforementioned conventional energy generation and storage technologies, there is a need to assess the potential of In-Situ Resources Utilization (ISRU) methods to enable or supplement long duration missions. We present a computational model (MATLAB) of a Thermal Energy Storage (TES) system coupled to drive a heat engine (Thermoelectric Generator) to produce electricity. The TES medium designed is based off processed lunar regolith, an abundant material present on the surface of the Moon. The architecture has been optimized to provide a minimum electrical power of 36 W per unit after 66 h of polar night, but the modular nature of the model allows other ranges of parameter to be simulated. A trade-off between this ISRU-based concept and conventional approaches for energy production and storage was performed and ranked TES and thermoelectricity generation as the least appropriate option. This result is valuable in a period of enthusiasm towards ISRU. It shows that processes exploiting extraterrestrial materials instead of Earth supplies are not systematically attractive. Despite the non-favorable performances for the proposed concept, some perspectives for the TES system are given as well as potential model improvements such as the need to assess the use of a Stirling heat engine

Correlation between surface damage and mechanical properties at micro- and nanometric length scale for WC-Co hardmetals

Cemented carbides (WC-Co) are ceramic-metal composite materials made by hard tungsten carbide particles bonded through a metallic binder matrix, mainly of cobalt. It is a hard material characterized by an exceptional combination of strength, toughness and wear resistance. As result, cemented carbides are first choice materials for cutting tools and wear parts. However, final shaping of these components usually require diamond grinding. During this hard machining, surface integrity may became altered, particulary in terms of compression stresses and/or microcracking. Such defects can locally affect the mechanical properties. The aim of this investigation is to analyze the influence of the surface finish quality on the mechanical properties at the surface level for WC-Co materials as well as the influence over the properties of a TiN coating deposited on hardmetal substrates. The study has been done at micrometric (to analyze the general properties) and nanometric scale (local properties aiming to capture residual stress state effects) by using nanoindentation and nanoscratch testing. Tests done in plain view prove that roughness plays an important role in the assessment of mechanical properties at the surface, as it induces significant scatter, as compared to results determined on cross-sections. Finally, a sequential polishing process has been done in order to extract the polishing rate for cemented materials as well as study how roughness affects the mechanical properties measured. This process points out that roughness can mask surface damage, like cracks or chipping, among others. As a final conclusion, an optimized protocol is proposed to study the mechanical properties of the samples with high roughness and exhibiting a compressive residual stress state

Correlation between surface damage and mechanical properties at micro- and nanometric length scale for WC-Co hardmetals

Cemented carbides (WC-Co) are ceramic-metal composite materials made by hard tungsten carbide particles bonded through a metallic binder matrix, mainly of cobalt. It is a hard material characterized by an exceptional combination of strength, toughness and wear resistance. As result, cemented carbides are first choice materials for cutting tools and wear parts. However, final shaping of these components usually require diamond grinding. During this hard machining, surface integrity may became altered, particulary in terms of compression stresses and/or microcracking. Such defects can locally affect the mechanical properties. The aim of this investigation is to analyze the influence of the surface finish quality on the mechanical properties at the surface level for WC-Co materials as well as the influence over the properties of a TiN coating deposited on hardmetal substrates. The study has been done at micrometric (to analyze the general properties) and nanometric scale (local properties aiming to capture residual stress state effects) by using nanoindentation and nanoscratch testing. Tests done in plain view prove that roughness plays an important role in the assessment of mechanical properties at the surface, as it induces significant scatter, as compared to results determined on cross-sections. Finally, a sequential polishing process has been done in order to extract the polishing rate for cemented materials as well as study how roughness affects the mechanical properties measured. This process points out that roughness can mask surface damage, like cracks or chipping, among others. As a final conclusion, an optimized protocol is proposed to study the mechanical properties of the samples with high roughness and exhibiting a compressive residual stress state