| 1. |
- Hernandez, Sinuhe, et al.
(författare)
-
High temperature friction and wear mechanism map for tool steel and boron steel tribopair
- 2014
-
Ingår i: Tribology - Materials, Surfaces & Interfaces. - 1751-5831 .- 1751-584X. ; 8:2, s. 74-84
-
Tidskriftsartikel (refereegranskat)abstract
- Tribological systems working under severe conditions like high pressures, sliding velocities and temperatures are subjected to different phenomena such as wear, oxidation and changes in mechanical properties. In many cases, there are several mechanisms occurring simultaneously.The predominating type(s) of wear mechanism(s) presented will depend on the materials in contact, operating parameters and surrounding environment. In this work, high temperature tribological studies of boron steel sliding against tool steel were conducted using a pin-on-disc machine under unlubricated conditions at five different temperatures ranging from 25 to 400C, three different loads: 25, 50 and 75 N (contact pressures of 2, 4 and 6 MPa respectively) and a sliding speed of 0.2 ms-1. Scanning electron microscopy/energy dispersive spectroscopy and X-ray techniques were used for analysing the resulting damage and tribolayers of the worn surfaces. Additionally, hardness measurements were carried out in a special hot hardness rig in the same temperature range as that used in pin-on-disc tests. The results have shown that for a given load, the wear rate of boron steel decreased as the temperature increased, reaching itslowest value at 400C at 50 N. In the case of the tool steel, it could be observed that at 200C and above, the wear rate decreased as the load increased. This behaviour is consistent with the formation of a protective oxidised layer initiated at 100C. At higher temperatures, such layers become more pronounced. The obtained data were finally used to construct a friction and wear mechanism map for this material pair that takes temperature and pressure into account.
|
|
| 2. |
- Hernandez, Sinuhe
(författare)
-
High Temperature Wear Processes
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Moving machine assemblies are increasingly exposed to extreme operating conditions involving high temperatures owing to demands on higher power densities, high performance/efficiency and extreme environments. The changes in surface and near surface properties of contacting surfaces caused by exposure to high temperature and deformation govern the occurrence of friction, wear and material transfer of the tribological system. However, these changes have not been thoroughly investigated. In order to enable development of new products and processes, there is a need for new knowledge pertaining to tribological phenomena occurring at elevated temperatures.One of the most commonly used engineering materials is steel as it offers a good compromise between performance and cost even at high temperatures. For example, prehardened (quenched and tempered) tool steels are commonly used in hot forming dies can also be employed in other technological applications involving elevated temperatures. Although the research pertaining to hot stamping, and high temperature tribology in general, has significantly grown during the last years there are still knowledge gaps that need to be bridged. Adhesion and abrasion have been identified as the most dominant wear mechanisms in high temperature tribological systems but the detailed understanding of the mechanisms is still inadequate.The objective of this work is therefore to obtain a deeper understanding of the tribological phenomena associated with adhesion and abrasion that takes place at high temperatures. Unidirectional sliding wear tests have been conducted in order to investigate the influence of contact pressure and temperature on the wear and friction characteristics of tool steel and boron steel pair. Tribological studies involving boron steel, tool steels and heat-treated high-Si steels in a three body abrasive environment were also carried out with a view to explore the effect of temperature on the wear rate, wear mechanisms and to correlate this with material properties like hot hardness and toughness.The results from the unidirectional sliding tests showed that the frictional behaviour of tool steel and boron steel is load and temperature dependent. In general the friction coefficient decreases as both temperature and load are increased as a result of the formation of oxide layers. At temperatures above 200 °C, the compaction and sintering of these layers led to the formation of a wear protective glaze layer. Consequently, the wear rate for both materials decreased at elevated temperatures. Additionally, a friction and wear mechanisms map was developed for the investigated materials.In the case of abrasive wear tests, the results showed that the main wear mechanism presented for each material varied with temperature. In general, a transition from micro-ploughing to a combination of micro-cutting and micro-ploughing was present. The tool steels and boron steel showed a decrease in wear rate in the range of 100 to 400 °C compared to that at room temperature. This was attributed to the toughness in case of the tool steel and the formation of a protective tribolayers for the boron steel. Above 400 °C the wear rate increased for these three materials mainly due to the recovery and recrystallization processes. The wear rate of the high-Si steels increased with testing temperature. At 500 °C, these steels had the same hardness and the differences in wear were attributed to the changes in the material toughness.
|
|
| 3. |
- Tomala, A., et al.
(författare)
-
Tribological performance of some solid lubricants for hot forming through laboratory simulative tests
- 2014
-
Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 74, s. 164-173
-
Tidskriftsartikel (refereegranskat)abstract
- Tribological research concerning sliding contacts at temperatures of 500–1000 °C has received limited attention. Industrial systems operating under high temperatures can be readily found in sheet metal forming processes. The control of friction during the tool-workpiece interaction and minimization of tool wear are both crucial in maintaining the products quality. The application of solid lubricants can be a possible approach in accomplishing these goals.The objective of this work is to investigate the reliability of combined model and component tests under solid lubricating conditions. The laboratory tests showed that both methodologies provide consistent results in exploring potential of the solid lubricants
|
|
