Search

Machining of carbon fibre reinforced polymer (CFRP) is abrasive and causes significant tool wear. The effect of tool wear on static flexural strength is investigated, using edge trimming with uncoated carbide and chemical vapour deposition (CVD) diamond coated burr style tools. Edge rounding (ER) criteria along with flank wear are used to observe tool degradation with ER shown to preferentially wear allowing the tool to become cyclically sharper and duller, corresponding to fluctuating dynamometer readings, a novelty for CFRP machining. Areal surface metrics degraded for an uncoated tool due to changes in cutting mechanism, whilst for up to 16.2 m of linear traverse, the coated tool showed limited changes. Tool wear, caused by edge trimming 7.2 m of CFRP, using an uncoated carbide tool, provided a flexural strength reduction of up to 10.5 %, directly linking tool wear to reduced mechanical strength. • Uncoated and coated tools showed cyclical sharpening of cutting edges which was reflected in cutting force measurements. • Edge radius of cutting tools obtained through focus variation are shown to be a useful metric to measure wear. • Worn, uncoated carbide tools lead to increased S a and reduced flexural strength compared to unworn. [ABSTRACT FROM AUTHOR]

Nickel aluminide coatings with three different compositions, namely δ-Ni 2 Al 3 , Al-rich β-NiAl and Ni-rich β-NiAl were produced by chemical vapor deposition on pure nickel with successive diffusion heat treatments. The influence of the coating composition on the wear resistance is systematically studied and discussed based on the stability region of the δ-Ni 2 Al 3 to the hypo-stoichiometric β-NiAl phase using a ball-on-disk setup up to 600 °C in air with alumina as the counterpart material. Wear resistance generally increased with decreasing Al contents of the coatings tested. Nanoindentation measurements showed that Young's moduli and hardness decreased for decreasing Al contents in the NiAl system. This change is accompanied with an increase in ductility, resulting in higher resistance against cracking of the coating, which is found to be the main wear mechanism for Al-rich coatings. • Wear resistance of NiAl coatings increased with decreasing Al content. • Wear resistance could be correlated to the mechanical properties of the coating. • Al-rich coatings improve tribologically over time due to Al depletion. • Wear debris at high temperatures forms glazes beneficial for the wear behavior. [ABSTRACT FROM AUTHOR]

Al-rich phases are often recommended as potential coating candidates for TiAl alloys and their application as a turbine blade material in aero engines. As high wear resistance is also required for this application, the tribological properties of Al-rich phases need to be investigated with a focus on the influence of temperature. Therefore, a comparative investigation of the dry sliding wear behavior of the uncoated and aluminized Ti–48Al–2Cr–2Nb TiAl alloy was conducted between room temperature and 600 °C in air. While the uncoated TiAl alloy suffers from successively increasing wear rates with increasing temperature, the aluminized alloy shows lower wear rates up to 400 °C. However, barely any positive influence on the required wear protection can be observed at 600 °C due to partial failure of the coating. Wear mechanisms of both the uncoated and aluminized samples are characterized by high material transfer to the counterpart material, the Ni-based alloy IN718. This phenomenon is caused by the tendency for strong adhesive bonding between the two metallic counterparts and becomes even more pronounced with increasing temperature. • Wear rates of the uncoated TiAl alloy increase with increasing temperature. • Material transfer from the TiAl alloy to the IN718 counterpart occurs already at RT. • Aluminizing leads to lower wear rates up to 400 °C due to a higher surface hardness. • Partial coating failure occurs at 600 °C leading to highly increased wear rates. • Aluminizing can also improve the oxidation resistance of TiAl turbine blades. [ABSTRACT FROM AUTHOR]

The ability to control the shape, distribution and composition of non-metallic inclusions has had an important impact on many aspects of steel making. One such impact is on the machinability. Ca-treatments have shown to be able to reduce the abrasiveness of oxide inclusions, improve chip-breaking and lead to formation of deposits that reduce tool wear. However, machining Ca-treated steels with Al 2 O 3 coated cemented carbide tools has not been as advantageous as expected. This study investigates the mechanisms behind the anomalous wear of Al 2 O 3 coatings when turning soft Ca-treated steels. Longitudinal turning tests at a range of speeds (v c = 100–600 m/min) show rapid localized degradation of the Al 2 O 3 coating limited to the sliding zone. Detailed analysis of the degradation mechanisms was performed using scanning and transmission electron microscopy. The results demonstrate a presence of chemical interactions between the alumina coating and non-metallic inclusions. The interaction resulted in the formation of mainly calcium aluminates and partly alumina-magnesia spinel. In-operando infrared thermography measurements indicate cutting temperatures of 850–1000 °C. Thermodynamic calculations give that CaO and MgO readily reacts with Al 2 O 3 , while the reaction with CaS requires presence of additional oxygen at these cutting conditions. Additional turning experiments investigate the influence of oxygen by controlling the cutting environment by adding oxygen (compressed air) or removing oxygen (supply argon). These additional tests show that the presence of additional oxygen has a limited impact on the possible Ca–Al 2 O 3 interaction. This demonstrat a potential for further machinability improvements by controlling the chemical interaction between Ca and Mg based non-metallic inclusions and alumina coatings. • The inertness of alumina coatings has previously been overestimated. • Ca and Mg based non-metallic inclusions can degrade Al 2 O 3 coatings. • (Ca,Mg,Al) x O y form between the coating and chip. • Atmospheric oxygen does not increase the rate of degradation. • Creating a possibility for further development of Ca-treatments. [ABSTRACT FROM AUTHOR]