Wear volume of self-mated steel at the submicron-scale: an AFM study

Wear phenomena at the nanoscale are essential for applications involving miniaturized specimens. Furthermore, stochastic nano-events affect in general tribological processes, eventually also at the macroscale. Hence, it is of fundamental importance to perform nanotests with materials – such as steel – which are widely used also at the macroscale. In this paper, we present the analysis of tribotests performed with self-mated 100Cr6 steel (AISI 52100) at the submicron scale by means of an atomic force microscope. To this aim, steel particles with micrometre size were glued to the cantilever as “colloidal particles”. The microscope was employed for wear generation, for the imaging of scars and colloidal particles, and for the determination of wear volumes of both specimens. The analysis is focused on wear volume and its dependence on normal force and total sliding distance. Nanotests are compared with previously presented macrotests, also performed with self-mated steel. Nanotests exhibit, compared with macrotests, a significantly larger scattering and poor repeatability. Especially the analysis of these features reveals that, with small forces (≤ 10 µN) and surfaces (≤ 2 µm2), the random number of asperities inside the contact surface plays a crucial role, by far more decisive than the normal force or the sliding distance. Moreover, in several cases, only few asperities (< 10) are involved in the wear process. Such low numbers lead to a breakdown in the applicability of tribological laws (e.g. Archard's law) based on statistical methods and on average variables.

Influence of the Deep Cryogenic Treatment on AISI 52100 and AISI D3 Steel’s Corrosion Resistance

The effect of deep cryogenic treatment (DCT) on corrosion resistance of steels AISI 52100 and AISI D3 is investigated and compared with conventional heat-treated counterparts. DCT’s influence on microstructural changes is subsequently correlated to the corrosion resistance. DCT is confirmed to reduce the formation of corrosion products on steels’ surface, retard the corrosion products development and propagation. DCT reduces surface cracking, which is considered to be related to modified residual stress state of the material. DCT’s influence on each steel results from the altered microstructure and alloying element concentration that depends on steel matrix and type. This study presents DCT as an effective method for corrosion resistance alteration of steels.

Microstructure and Wear Behavior of TiC/AISI 1020 Metal Matrix Composites Produced by Liquid Pressing Infiltration

A metal matrix composite was developed through a unique liquid pressing infiltration process to study the wear mechanism of a TiC reinforced AISI 1020 steel matrix. The microstructure, hardness, and wear behaviors of the TiC/AISI 1020 composite were compared with commercial AISI 52100 bearing steel. Microstructural analysis showed that there were no defects, such as pores or agglomeration of reinforcement particles, and about 60% of the volume of TiC was uniformly dispersed. In the case of the AISI 52100 alloy, the hardness was 62.42 HRC, which was similar to the 62.84 HRC value of the as-cast TiC/AISI 1020 composite. After the quenching heat treatment, the Rockwell hardness of the composite increased to 76.64 HRC, which was attributed to the martensitic transformation of the AISI 1020 matrix. As a result of the pin-on-disc wear test with high contact pressure, the wear width of AISI 52100 was 2937 μm, which was approximately 4.3 times wider than that of the heat-treated metal matrix composite (682 μm). The wear depths of AISI 52100 and the heat-treated composite were 2.6 μm and 0.5 μm, respectively, indicating that TiC/AISI 1020 exhibited excellent wear resistance compared with bearing steel. Improved wear resistance of the TiC/AISI 1020 composite originates from uniformly distributed TiC, with an increase in the hardness due to the heat treatment.

Tribological Properties and Corrosion Resistance Properties of NbN/TiN Multilayer, TiNb-NX Single-Layer and Coatings that are Doped with Carbon

NbN/TiN, TiNb-NX and CH-TiNb-N12 coatings are deposited by RF magnetron sputtering to determine the tribological properties and corrosion resistance. ‘x’ is the flux rate for nitrogen and ‘CH’ signifies the addition of acetylene. In terms of the corrosion resistance, all the coatings have a similar corrosion potential and NbN/TiN multilayer coatings exhibit the lowest corrosion current. The NbN/TiN multilayer has a low pitting potential so severe pitting corrosion is observed on the surface. CH-TiNb-N12 coating is most resistant to corrosion and exhibits no pitting before the test ends. In contact with counter-bodies with a Si3N4 ball or an AISI 52100 ball, a CH-TiNb-N12 coating acts as a solid lubricant so the wear mechanism shows the least abrasion. The CH-TiNb-N12 coating has the lowest wear rate and coefficient of friction for sliding against Si3N4 and AISI 52100 balls. The wear rate is respectively 3.2 and 6.8 times less than that for SKH51 substrate when sliding against Si3N4 and AISI 52100 balls. The results for this study show that a TiNb-N12-CH coating has the best tribological properties and corrosion resistance.

Austempering and Bainitic Transformation Kinetics of AISI 52100

AISI 52100 is a high carbon alloy steel typically used in bearings. One hardening heat treatment method for AISI 52100 is austempering, in which the steel is heated to above austenitizing temperature, cooled to just above martensite starting (Ms) temperature in quench media (typically molten salt), held at that temperature until the transformation to bainite is completed and then cooled further to room temperature. Different austempering temperatures and holding times will develop different bainite percentages in the steel and result in different mechanical properties. In the present work, the bainitic transformation kinetics of AISI 52100 were investigated through experiments and simulation. Molten salt austempering trials of AISI 52100 were conducted at selected austempering temperatures and holding times. The austempered samples were characterized and the bainitic transformation kinetics were analyzed by Avrami equations using measured hardness data. The CHTE quench probe was used to measure the cooling curves in the molten salt from austenitizing temperature to the selected austempering temperatures. The heat transfer coefficient (HTC) was calculated with the measured cooling rates and used to calculate the bainitic transformation kinetics via DANTE software. The experimental results were compared with the calculated results and they had good agreement.

Machining force comparison for surface defect hard turning and conventional hard turning of AISI 52100 steel

In this article, a recently developed method called surface defect machining (SDM) for hard turning has been adopted and termed surface defect hard turning (SDHT). The main purpose of the present study was to explore the impact of cutting parameters like cutting speed, feed, depth of cut, and tool geometry parameters such as nose radius and negative rake angle of the machining force during surface defect hard turning (SDHT) of AISI 52100 steel in dry condition with Polycrystalline cubic boron nitride (PCBN) tool; and results were compared with conventional hard turning (CHT). Experimentation is devised and executed as per Central Composite Design (CCD) of Response Surface Methodology (RSM). Results reported that an average machining force was decreased by 22% for surface defect hard turning (SDHT) compared to conventional hard turning (CHT).