Tribocorrosion is an irreversible transformation of a material resulting from simultaneous physico-chemical and mechanical surface interactions in a tribological contact. Electrochemical methods are well suited for the study of tribocorrosion phenomena because they allow one to simulate the corrosive effect of the environment by imposing a fixed potential. Furthermore, the measurement of the anodic current permits one to determine the amount of material removed by oxidation as opposed to mechanical wear. In the present paper, experimental and theoretical aspects of applying electrochemical methods in tribology are discussed and recent results obtained with passivating metals in the authors' laboratory are presented. The importance of controlling the mechanical parameters and the contact geometry is stressed, and it is shown that these parameters can significantly affect the electrochemical response of a tribocorrosion system.

Electrochemical methods in tribocorrosion: a critical appraisal

Eco-friendly geopolymer prepared from solid wastes: A critical review.

Geopolymer is a new environment-friendly cementitious material, and the development of geopolymer can reduce the carbon dioxide emission caused by the development of cement industry. Geopolymer materials not only have excellent mechanical properties, but also have a series of excellent properties such as fire resistance and corrosion resistance. Most industrial solid waste and waste incineration bottom ash are piled up at will, which not only occupies land resources, but also has a bad impact on the environment. Recycling them can be used as raw materials for preparing geopolymers. Geopolymer materials can effectively adsorb heavy metals, dyes, and other radioactive pollution, which is very beneficial to society's future development. However, due to the excellent properties of geopolymer materials, its application goes beyond that. Some useful information about geopolymer materials was introduced in this paper. The paper included the geopolymerization, the source of raw materials, the types of activators, the preparation methods, and the different application fields of geopolymer materials. The factors affecting the fresh properties and mechanical properties of geopolymer materials were discussed. In this paper, the shortcomings and application limitations of geopolymer materials were summarized, and their progress was summarized to lay a theoretical foundation for the long-term development of geopolymer materials.

Advances in geopolymer materials: A comprehensive review

This paper presents an efficient application for red mud, i.e., recycling red mud as a mineral additive in the development of ultra-high performance concrete (UHPC). Specifically, the modified Andreasen & Andersen particle packing model has been carried out to obtain a densely compacted UHPC matrix. After that, red mud is used to replace cement to reduce both the landfilling of red mud and the environmental burden of UHPC. Then, the fresh and hardened behavior of UHPC with and without red mud has been evaluated. It has been found that the addition of red mud enhanced early-age (7 d) durability due to the accelerated hydration process, while reduced the workability and the mechanical properties of UHPC. The degraded workability may affect the application in the building with complex shapes, but it can still be applied in general construction. An ultra-high strength (>150 MPa) of UHPC including 40% red mud can be generated after high-temperature curing, although the addition of red mud reduces the compressive strength. Besides, it is noteworthy that significantly shortened setting time can be obtained when replacing cement by red mud, providing ideas for the application in the UHPC rapid-repairing process. The pore structure analysis reveals a coarsening of micro-pore structure with an increase of red mud content. Finally, a low-energy consumption, as well as low radiation risk further promotes the environmental protection application of red mud based UHPC.

Sustainable use of red mud in ultra-high performance concrete (UHPC): Design and performance evaluation

Polyvinyl alcohol (PVA) fiber-reinforced geopolymer mortar is an eco-friendly construction material with excellent mechanical properties and durability. Visual observation, mass loss measurement, cubic and prism compressive tests , flexural tests, thermogravimetric and differential thermal analysis , scanning electron microscopy, and bubble parameter tests were conducted to evaluate the effect of PVA fiber and exposure temperature on the behavior of PVA fiber-reinforced geopolymer mortar after exposure to high temperatures. The PVA fiber contents were selected as 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%, and the target temperatures were 25 °C, 200 °C, 400 °C, 600 °C and 800 °C. The results indicate that significant mass loss of the geopolymer mortar could be observed when the exposure temperature increased from 25 °C to 250 °C, whereas slight mass loss occurred from 250 °C to 700 °C, and no mass loss was detected from 700 °C to 800 °C. As the temperature increased, the geopolymer mortar gradually densified, while the geopolymer mortar continuously developed more cracks and pores. The compressive and flexural strengths of the geopolymer mortar improved as the temperature increased from 25 °C to 200 °C, but it decreased significantly as the temperature further increased to 800 °C. In addition, on exposure to 200 °C, the presence of PVA fibers significantly improved the cubic and prism compressive strengths and flexural strength by 50.5%, 29.4%, and 66.3%, respectively, compared with the geopolymer mortar without fibers. As the temperature increased above 200 °C, although the PVA fiber decomposed, the defects left by the melt fibers slightly influenced the strength of the geopolymer mortar. 

High-temperature behavior of polyvinyl alcohol fiber-reinforced metakaolin/fly ash-based geopolymer mortar

Preparation of a geopolymer from red mud slurry and class F fly ash and its behavior at elevated temperatures

In this study, the effects of microstructure, surface roughness, and surface porosity on the corrosion behavior of direct metal laser sintered (DMLS) Ti-6Al-4V were experimentally investigated The electrochemical measurements were conducted using a three-electrode setup setting, with the specimens in Ringer’s solution at 37 °C The acicular microstructure in the DMLS Ti-6Al-4V samples resulted in greater corrosion resistance than that of the Grade 5 alloy with an equiaxed microstructure Electrochemical study results indicated that microstructure and surface roughness had a significant influence on the corrosion behavior of the samples Pits and cracks were observed near the edges of the original surface pores in the as-printed samples after a 1-month immersion in simulated body fluid The results showed that the acicular microstructure with a small number of surface pores and a smooth surface led to more desirable corrosion resistance

Factors Influencing the Corrosion Behavior of Direct Metal Laser Sintered Ti-6Al-4V for Biomedical Applications

In this work, a machine-learning model was established to predict the influence of post-treatment, hot isostatic pressing (HIP) parameters on the tensile properties of Ti6Al4V parts prepared by Laser Powder Bed Fusion (LPBF), also known as Selective Laser Melting (SLM). The database was established by collecting published reports on HIP treatment of LPBF Ti6Al4V from 2010 to 2019, employing the following online resources: Google Scholar, Science Direct, Research Gate, and Springer. Using the established model, it is possible to prescribe HIP parameters and predict properties after HIP for LPBF Ti6Al4V parts with high confidence. The model shows great accuracy in the prediction of Yield Strength (YS) and Ultimate Tensile Strength (UTS). Of the predictions, 87.5% were within a 5% error range for YS in all datasets, and this value was 100% for UTS. It was found that the YS and UTS are sensitive to the HIP parameters, including temperature and holding time. The initial YS and UTS of as-printed parts are weaker influencing factors for YS and UTS of final parts, as compared with the HIP parameters. The model suggests that a HIP process with a holding temperature lower than 970°C and a holding time of approximately 2 hours is sufficient for LPBFed Ti6Al4V parts to achieve mechanical properties that comply with the ASTM standard of Ti6Al4V for surgical implant applications (Standard Specification for Wrought Titanium-6Aluminum-4Vanadium ELI (Extra Low Interstitial) Alloy for Surgical Implant Applications -UNS R56401-). However, the prediction of strain to failure showed lower accuracy. Only 62.1% of predicted strain results were within a 10% error range. The differences among the printing processes by multiple research groups may have resulted in large variations of structural defects and thus led to significant scattering of the elongation data. The model also shows that elongation after HIP has a higher dependence on the as-printed samples. 

A Machine-Learning Model to Predict Tensile Properties of Ti6Al4V Parts Prepared by Laser Powder Bed Fusion with Hot Isostatic Pressing

Abstract In this work, an artificial neural network model is established to understand the relationship among the tensile properties of as-printed Ti6Al4V parts, annealing parameters, and the tensile properties of annealed Ti6Al4V parts. The database was established by collecting published reports on the annealing treatment of selective laser melting (SLM) Ti6Al4V, from 2006 to 2020. Using the established model, it is possible to prescribe annealing parameters and predict properties after annealing for SLM Ti-6Al-4V parts with high confidence. The model shows high accuracy in the prediction of yield strength (YS) and ultimate tensile strength (UTS). It is found that the YS and UTS are sensitive to the annealing parameters, including temperature and holding time. The YS and UTS are also sensitive to initial YS and UTS of as-printed parts. The model suggests that an annealing process of the holding time of fewer than 4 h and the holding temperature lower than 850°C is desirable for as-printed Ti6Al4V parts to reach the YS required by the ASTM standard. By studying the collected data of microstructure and tensile properties of annealed Ti6Al4V, a new Hall-Petch relationship is proposed to correlate grain size and YS for annealed SLM Ti6Al4V parts in this work. The prediction of strain to failure shows lower accuracy compared with the predictions of YS and UTS due to the large scattering of the experimental data collected from the published reports.

Machine learning model to predict tensile properties of annealed Ti6Al4V parts prepared by selective laser melting

Domain-specific big data poses issues in knowledge discovery and decision support given its many Vs such as volume, variety, and visualization. In this work, we propose solutions via Ishikawa diagrams, JESS (Java Expert System Shell) with rule discovery, as well as visual analytics. We deploy data science and domain models, targeting engineering and scientific domains. Our results yield high accuracy, efficiency and cost-effectiveness.

Zhaotong Yang

Papers

Preparation of a geopolymer from red mud slurry and class F fly ash and its behavior at elevated temperatures

Factors Influencing the Corrosion Behavior of Direct Metal Laser Sintered Ti-6Al-4V for Biomedical Applications

A Machine-Learning Model to Predict Tensile Properties of Ti6Al4V Parts Prepared by Laser Powder Bed Fusion with Hot Isostatic Pressing

Machine learning model to predict tensile properties of annealed Ti6Al4V parts prepared by selective laser melting

Ishikawa, JESS, and Visual Analytics for Engineering