Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr)₂C-7%Ni, Cr₃C₂-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10^?6 mm³/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.     

High temperature tribology of ceramics

The friction and wear behaviour of self-mated couples of MgO---ZrO₂, Al₂O₃ and two types of SiSiC were studied under dry sliding conditions in a special pin-on-disc high temperature tribometer. The temperature was varied between 25 and 1000°C, and the sliding speed from 0.03 m s⁻¹ to 3 m s⁻¹. The morphology of the worn surfaces was studied by means of SEM, and their phase distribution by X-ray diffraction and TEM analyses. The results show that the wear coefficients of all couples mostly increase with increasing temperature and sliding velocity. The wear of MgO---ZrO₂ is influenced by tribo-induced phase transformations while α-Al₂O₃ retains its original structure for all test conditions. For SiSiC delamination and fatigue of the interface Si/ß-SiC predominate. At higher temperatures and sliding velocities tribo-oxidation is effective. The friction coefficients lie between 0.5 and 1.0 under steady-state conditions but for short test durations lower values can occur. The couple SiSiC/SiSiC has low friction coefficients at low sliding velocities and temperatures, even if the steady-state region is reached.     

聚酰胺染色过程中的pH控制

酸性产及金属络合染料对聚酰胺染色通常都使用温度控制方法。温度的控制一般基于经验,并且常根据织物质量,色泽深度及使用设备来加以选择。在ＰＨ恒定工艺中这些裼 最优化过去已经描述过。为了增加染浴的竭染率并由此来改善染色的重现性和资源匀染性,在工艺操作中实施降低ＰＨ同时井高温度是切实可行的。要一文就这类ＰＨ滑动工艺的最优化作了概念。由于最佳的ＰＨ范围随着没的被染物而改变,因而本语文所述的方法也考虑到了这些     

Triboactive materials for dry reciprocating sliding motion at ultra-high frequency

High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 μm and 5 μm. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set-ups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Ti_n?2Cr₂O_2n?1 and Ti_nO_2n?1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 10¹¹ cycles. Very low wear rates in the range 10^?8 mm³/Nm down to 10^?10 mm³/Nm were determined under dry oscillation in air.     

INFLUENCE OF MACHINING ON FRICTION AND WEAR OF LUBRICATED CERAMICS IN SLIP-ROLLING CONTACTS

Abstract

The slip-rolling friction and wear tests were performed in a twin disc tribometer of the Amsler-type at a Hertzian pressure of 3 GPa over 2 million revolutions. Paraffinic oil with no additives was used as lubricant. The ceramics were machined with different processes, resulting in different surface roughness (i.e., rough and fine honed, rough and fine ground, rough and fine lapped, and rough and fine polished). Ceramic materials like HIP-Si₃N₄, S-SiC, HIP-ZrO₂, and GPS-Si₃N₄-TiN were investigated as self-mated couples. This paper summarizes the results. Si₃N₄, Si₃N₄-TiN, and ZrO₂ generally exhibit a small wear coefficient in the range of 10^?9 mm³/Nm in paraffinic oil and their wear coefficients correlate with the initial surface roughness and the material removal rate. The lowest wear coefficients were exhibited by ZrO₂- With a reduction of the Hertzian pressure to 1.5 GPa, S-SiC exhibits the same tribological behavior as the other ceramics.