ISSN   1004-0595

CN  62-1224/O4

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柱塞泵滑靴副Cu-Sn-Bi合金的摩擦学性能

The Tribological Properties of Cu-Sn-Bi Alloy for Slipper Pair of Plunger Pump

  • 摘要: 采用粉末冶金工艺在钢背底上烧结了2种不同Ni含量(质量分数为0%和2%)的铜锡铋(Cu-Sn-Bi)双金属复合材料,研究了复合材料合金铜层密度、布氏硬度、微观组织和不同环境温度(25、70、100和150 ℃)下的摩擦学性能. 结果表明:Ni强化后的复合材料密度和表面硬度均有所提高;合金表面孔洞减少,晶粒细化作用明显,这归因于Ni加入合金中引起的再结晶反应;拉伸断口处的小韧窝提高了合金的断裂韧性;相对于未经Ni强化的Cu-Sn-Bi,摩擦试验中含质量分数2% Ni的Cu-Sn-Bi复合材料在温度较低时有更稳定的摩擦系数和更长的摩擦寿命,这得益于强化后的合金磨痕表面形成了1种耐磨层;在温度较低时,耐磨层主要由磨痕表面的轻微塑性变形层和吸附的NiO氧化层组成;在温度较高时,耐磨层主要由磨痕表面均匀涂覆的Fe2O3和Fe2O4组成;此外,强化后的Cu-Sn-Bi合金大幅减少了在干摩擦过程中剥落的磨屑数量,使其更适合用于闭式机械设备中;Ni强化后的合金试样在缺油润滑状态下能更平稳的进入混合弹流润滑阶段.

     

    Abstract: Powder metallurgy was used to prepare two types of copper-tin-bismuth (Cu-Sn-Bi) composites with different Ni contents (mass fraction 0% and 2%) on SPCC (Steel Plate Cold rolled Commercial). Copper alloy layer density and Brinell hardness were measured. The composite microstructure was observed by metallographic microscopy and EBSD (Electron Backscattered Diffraction). The self-lubricating properties of two samples were investigated at different environmental temperatures (25, 70, 100 and 150 ℃). Their tribological properties under oilless conditions were also evaluated. The results showed that the addition of Ni increased the density of the Cu-Sn-Bi composite from 7.94 g/cm³ to 8.19 g/cm³, and the Brinell surface hardness increased from 56.5 to 66.2. A significant increase in matrix density was the result of pore reduction on the surface of copper alloy. Copper alloy composites showed significant grain refinement, including increased small-angle grains. It was attributed to the recrystallizing reaction caused by adding Ni to the alloy, which may improve the overall mechanical properties of the material. The morphology of the pits at the tensile fracture surface of the copper layer was significantly different. Strengthening results in smaller pits in the alloy, which reduced its brittleness and improved its surface toughness. Friction tests were performed under dry conditions using a force of 50 N, a sliding speed of 0.125 m/s and at four different ambient temperatures. The Ni-reinforced Cu-Sn-Bi alloy had a more consistent friction coefficient at lower ambient temperatures and a longer service life at higher temperatures. As the temperature increased, the wear rate of the pre-strengthened sample gradually increased, while the wear rate of the strengthened alloy sample decreased. The wear rate of the pre-strengthened alloy material was 2.642×10−5 mm3/(N·m), which was 2.17 times higher than that of the strengthened material 1.217×10−5 mm3/(N·m) at an ambient temperature of 150 ℃. The above phenomenon occurred due to the formation of a wear-resistant layer on the worn surface of the strengthened alloy sample. At low temperatures, the wear-resistant layer was mainly composed of a slightly plastic deformation layer and an adsorbed NiO-oxide layer on the surface of the wear track. At high temperatures, the wear-resistant layer was mainly composed of Fe2O3 and Fe2O4 uniformly coated on the surface of the wear track. Furthermore, the strengthened Cu-Sn-Bi alloy greatly reduced the amount of debris that was peeled off during the dry friction process. This significantly reduced the wear damage caused by debris on the friction pair, while minimizing debris contamination in lubricated friction. This indicated that the alloy had good application potential in closed mechanical equipment. The Stribeck curve showed that the Ni-reinforced Cu-Sn-Bi alloy sample could enter the mixed EHL (Elasto hydrodynamic lubrication) stage faster and smoother in an oilless lubrication condition. This meat that the Cu-Sn-Bi bimetallic alloy material reinforced with 2% Ni could achieve good wetting compatibility under oilless lubrication conditions. This helped to reduce wear problems and improve the service life of friction pairs.

     

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