Over the years, fretting has been a leading cause of fuel failures for water cooled nuclear reactors. Implementation of liquid lead coolant increases the need for fretting and corrosion-resistant materials. Fe–10Cr–4Al alloy has shown good resistance to thermal aging, oxidation, liquid metal corrosion, and embrittlement in liquid lead environment. The performance of Fe-10Cr-4Al under fretting wear conditions has not been studied previously. This work aims to investigate the fretting wear and friction behaviour of self-mated Fe-10Cr-4Al alloy at varying temperatures, in the presence of a reducing gas environment and liquid lead. The results show that an increase in test temperature from RT to 550 °C decreases the coefficient of friction and promotes the formation of Cr and Fe oxide third body layer. At high temperature in reducing gas atmosphere, the initial plastic deformation and severe adhesion leads to early seizure. Presence of liquid lead has a lubricating effect and allows a third body layer to form on worn surfaces. A detailed description of the initial wear mechanisms of Fe-10Cr-4Al alloy and friction levels under various conditions provides a base for further investigation of this alloy for long-duration fretting wear.

There is a great potential in using different techniques of additive manufacturing (AM) for the production and refurbishment of hot forming dies. In hot stamping of AlSi-coated boron steel, the dies are exposed to a complex combination of abrasive and adhesive wear. This results in tool damage and eventually tool refurbishment is necessary. Laser-metal-deposition (LMD) is an AM technique suitable for tool repairing due to its easier implementation, compared to selective-laser-melting (SLM). However, tribological studies on AM produced tools are still limited, particularly in the context of hot forming. Thus, the aim of this work is to increase the knowledge on the friction and wear behavior of LMD tool materials in hot stamping conditions. Two LMD materials were investigated: a hot-work tool steel (LMD-TS) and a conceptual high-hardness tool material (LMD-HH). Porosity was observed for both materials in the form of lack-of-fusion defects. LMD-TS resulted in a Vickers hardness value of approximately 650 HV, while LMD-HH showed a value of approximately 1100 HV. A high temperature strip drawing tribometer was used to perform friction and wear tests against AlSi-coated boron steel under unidirectional (linear) sliding conditions. Workpiece temperatures during sliding were 600 °C and 700 °C. All tribotests at 700 °C resulted in severe adhesion and AlSi-coating rupture, resulting in higher and more unstable friction. The wear mechanisms observed for LMD-TS were a combination of abrasive and adhesive wear, where ploughing and grooving in the tool material resulted in larger surface defects to accumulate material transfer. At 700 °C, these mechanisms were more severe. LMD-HH did not show significant abrasive damage in any test; the resulting material transfer was thinner and sparser compared to the other LMD material. The change in FeAlSi material transfer for LMD-HH was associated with the reduction in abrasive damage, i.e., ploughing and grooving in the tool material did not take place and thus did not enhance material transfer. The LMD process itself did not seem to have either a positive or a negative effect on the tribological behavior of the tool materials in this tribosystem, and the differences are seen mostly from the hardness perspective. LMD-HH is a promising tool material to reduce wear in hot stamping dies.

This work investigates the quantitative effect of the hydrogen concentration of 100Cr6 bearing steel on the surface-initiated damage induced during lubricated rolling/sliding tribotesting. Hydrogen was introduced to the samples prior to tribotesting by electrochemical pre-charging, and hydrogen concentration was measured using thermal desorption analysis. The surface-initiated damage was quantified by optical profilometry and scanning electron microscopy. An upper limit for the critical hydrogen concentration was determined to be 1.4–2 wppm diffusible hydrogen. At this concentration, the area fraction covered by damage features was found to double compared to uncharged samples. As both charged and uncharged samples exhibited the same type of surface damage (early-stage micropitting), it was concluded that hydrogen did not change the wear mechanism but decreased the number of contact cycles necessary for the initiation of surface defects.

This study investigate the effects of temperature on the tribological properties of Titanium-zirconium-molybdenum (TZM). TZM alloy was subjected to sliding contact against AISI 430 steel counterparts at varying temperatures. The results shows, the coefficients of friction (COF) at interface were 0.77, 0.75, 0.71, and 0.69, in the case of 25 °C, 300 °C, 600 °C, and 900 °C test temperatures. The presence of MoO3 and Mo9O26 phases suggested the wear resistance and decreasing COF at high temperature. Temperature is a critical factor influencing material transfer between TZM and AISI 430 steel. The primary TZM wear mechanism at 25 °C involved scratching, surface deformation, and local cracks, while elevated temperatures near 900 °C intensified material adhesion phenomena with a surface shearing effect on the TZM surface after the trotest.

Additive manufacturing (AM) of ferrous alloys has achieved a technological maturity level that allows for the production of high-performance steel components. Among these alloys, tool steels and maraging steels can be used in die manufacturing for different hot forming processes as both materials have good mechanical properties and thermal stability. In recent years, several works have successfully produced these alloys through selective laser melting, focusing on the optimization and characterization of their microstructure and mechanical properties. However, few studies look into the tribological aspects of these newly produced materials and even fewer consider high temperature friction and wear performance. Therefore, there is a need to understand the high temperature tribological response of tool materials produced by additive manufacturing. In this context, the aim of this work is to investigate the tribological behavior of a tool steel and a maraging steel, both produced by selective laser melting, at different elevated temperatures. A conventionally produced tool steel was used as reference. A reciprocating sliding tribometer was used to perform tests at 40 °C, 200 °C and 400 °C. The counter-body was a WC-Co cemented carbide. Friction and wear of the AM tool steel and reference tool steel were very similar, thus no signs of the AM route having an impact on the tribological behavior were observed. Both tool steels showed reduced wear volume with increasing temperature, while the opposite was observed for their respective WC-Co counter-bodies. Higher temperature also resulted in increased amount of W transferred onto the tool steel wear scars. AM maraging steel showed higher and more unstable friction level, as well as a much larger wear volume at all temperatures; material transfer onto WC-Co was observed at certain temperatures. Overall, tribolayer formation (or lack thereof) was the dominant aspect in the tribological responses.

Hot stamping is a forming process widely used in the manufacturing of structural components in automobiles. It is a versatile process that enables the fabrication of complex-shaped components with high strength. It also facilitates the manufacturing of components that incorporate high-strength sections and high-ductility sections, by controlling the cooling rate. The process is versatile in terms of the microstructures and mechanical properties that can be obtained. This versatility, however, puts high demands on the materials pertaining their stability, wear resistance, costs, etc. This study has focused on understanding the effect of temperature on the tribological response of different tool materials when these are exposed to high temperatures. The results show that friction significantly stabilises with increased temperature for most tool steels. One tool steel behaves more unstably at high temperature, and this is attributed to the presence of Cr7C3, MoO3, and VO and severe wear on the workpiece material. The most severe wear on the workpiece is caused by a partially melted interdiffusion layer, which facilitates the detachment of the Al-Si coating and subsequent transfer onto the tool; this effect is maximised at the highest temperatures of the workpiece. An important finding is that friction and material transfer severity decrease as the workpiece temperature decreases, and friction is stabilised as tool temperature increases without minimising wear or the average friction coefficient.

As hydrogen reduces the fatigue life of 100Cr6 bearing steel significantly, extensive research on the interaction of hydrogen with 100Cr6 is necessary. This study investigated the influence of rolling/sliding tribotesting performed on a micro-pitting-rig on the hydrogen absorption and trapping behaviour of 100Cr6 bearing steel. Thermal desorption mass spectrometry was used to compare the hydrogen desorption spectra of 100Cr6 samples after tribological tests and static heated oil-immersion tests to untested reference samples. The approach was chosen to further understand the influence of both microstructural deformation as well as steel-oil contact on the hydrogen absorption and trapping behaviour of 100Cr6. The tribological test showed a stable friction behaviour and mild wear which was dominated by local plastic deformation of surface asperities. Despite the mild wear, a change in de-trapping temperatures was found for tribotested samples compared to oil-immersed and untested reference samples. This finding indicates that even mild tribotesting conditions alter the hydrogen trapping behaviour of 100Cr6 bearing steel.

The increasing interest in liquid metal cooled nuclear reactors provides technical and scientific challenges such as the understanding, prevention, and prediction of the degradation of materials in liquid lead. Critical components include the fuel rods, heat exchanger tubes, and pump impellers. These functional elements are exposed to mechanical loading (up to 40 MPa), high temperatures (450–550 °C), and fluid-induced vibrations (up to 25 Hz). Under such conditions, fretting wear occurs between e.g., the spacer wire and the outer surface of the fuel or heat exchanger tubes. This work is aimed to establish a laboratory-scale fretting wear test setup and develop test methodology to enable systematic material characterisation in liquid metal environments. The results obtained by using the described methodology indicate that adhesive wear is the dominant degradation mechanism, and 316L stainless steel shows a higher coefficient of friction but a lower wear volume/tribolayer volume compared to 100Cr6 bearing steel. These results are in agreement with those reported in open literature and demonstrates the suitability of the presented method for conducting fretting tests and analysis for various materials and contact configurations in liquid lead environment.