，题号nx2020000162
TRIBOLOGY OF AISI ACD 0cr15Ni7Mo2Al(PH15–7MO) HIGH TEMPERATURE MECHANICAL PROPERTIES
Abstract
The tribological properties of the AISI ACD 0Cr15Ni7Mo2Al (PH15–7Mo) high temperature alloy was investigated by assessing its friction, wear resistance and deposition behaviour. The experimental tests revealed that the alloy exhibited a high frictional behavior against the steel counterpart for both rotation and reciprocating sliding regimes. The wear resistance of the alloy against the steel counter partner increased with increasing speed, but decreased with respect to temperature, over a range from 20 to 600˚C. Deposition of iron-complexes was found on the wear surface of the alloy. The result indicated that the frictional performance of the alloy was affected by the presence of the oxygen and iron-complexes. The knowledge obtained from this study is beneficial for the selection of suitable materials for various wear applications involving high temperature.
1. Introduction
Tribology is defined as the study of friction, wear and lubrication of surfaces in motion that are generally used in constructions materials, Kargar (2008). Tribology of wear parts determine their availability and performance and plays a critical role in wear behavior and performance of machines and engines, Kwon and Kwack (2013). Initially, investigation on tribology mainly focused on material systems that withstand with moderate loads and moderate temperatures. But tribology research extended towards materials that can withstand with higher temperatures, Zacharia et al. (2000).
AISI ACD 0Cr15Ni7Mo2Al (PH15–7Mo) is a high temperature alloy which is widely used in automotive and aircraft industries, Berardi et al. (2004). This alloy have good resistance to high temperature and oxidation and corrosion resistance. But studies on frictional and wear behavior of PH15–7Mo is very limited. Thus, the present work aims to study the tribological properties of the aforementioned alloy under high temperature using rotation and friction tests. The results obtained from this study can provide useful engineering insight at selecting suitable alloys for high temperature tribological applications.
2. Materials and Method
Materials
The study material is a high temperature, high performance alloy AISI ACD 0Cr15Ni7Mo2Al (PH15–7Mo) which is widespread used in particularly in automotive and aerospace industries, Berardi et al. (2004). The other partner material is a carbon steel which is usually used for tribology tests in many tribological studies.
Instrument for tribology tests
The friction and wear tests were conducted in a MFP-‐3 tribometer from BMC MessSysteme as represented in Figure. 1. The tribometer has rotational and linear capabilities and is equipped with a digital computer for controlling the generated forces and speed. The tribometer has the ability for testing materials at a range of temperatures.
Experimental procedure
Rotational tribology test
The rotational tribology test was conducted with following parameters: pressure 0.301MPa, normal load 5N, temperature 20˚C, speed 250 rpm, and sliding distance 5 km.
Reciprocating sliding tribology test
The reciprocal sliding tribology test was conducted with following parameters: pressure 0.301MPa, normal load 5N, temperature 20˚C, speed 0.5 m/s and sliding distance 5 km.
Wear morphology
The worn surfaces of the materials were observed taking optical micrographs which were taken by optical microscope (CEL AX-‐50).
3. Results and Discussion
Rotational tribology
The evaluated frictional force of the PH 15-7Mo alloy against the steel counterpart was obtained over the ranges speed from 10-250 rpm and temperature from 20-600. Figure. 2 showed that the frictional coefficent of the alloy against the steel counter partner showed the highest values (0.008-‐0.011) at 10 rpm. The frictional coefficient increased with increment of the speed. On the other hand, the frictional coefficient of the alloy increased with decreasing temperatures up to 400 ˚C and then decreased at higher temperatures (600 ˚C).
Reciprocating sliding tribology
Figure 3 showed the value of frictional coefficient of PH 15-‐7Mo against carbon steel over a range from 0.5 to 2 m/s. The result indicated that the frictional coefficient of PH 15-‐7Mo decreased with increasing speed up to 0.8 m/s and then increased with speed (Figure. 4).
Wear
Figure 4 displayed the wear rate of the PH 15-7Mo alloy against the carbon steel counterpart. It was found that the wear rate increased with elevation of temperature whereas decreased as the speed increased (Figure. 5).
4. Conclusion
The frictional performance of PH15–7Mo alloy was investigated by conducting both rotation and reciprocating sliding tribology tests using a MFP-‐3 tribometer. The results revealed that the frictional coefficient of the alloy increased with increasing speed (10-250 rpm and 0.5-2 m/s, respectively). Also the frictional coefficient of the alloy decreased with increasing temperature up to 400 ˚C and then increased further. The wear rate of the alloy was found to increase with temperature and decreased with increasing speeds. The formation of iron- complex on the wear surface of the alloy shows that the frictional performance of the alloy was affected by the presence of these complexes. The results of this study provide valuable knowledge for selecting suitable materials for various tribological application at high temperature.
