喷射沉积Cu-7.5Ni-2.5Sn合金组织性能的研究

采用喷射沉积技术制备Cu-7.5Ni-2.5Sn合金,分析其显微组织与性能,并与熔铸态同类合金比较。研究结果表明:喷射沉积Cu-7.5Ni-2.5Sn合金具有细小的等轴晶组织,Sn分布较均匀,熔铸Cu-7.5Ni-2.5Sn合金为发达的树枝晶组织,Sn在晶界严重偏析;二种不同工艺制备的合金性能比较,喷射沉积合金具有更加优异的性能,其硬度、抗拉强度(σb)、屈服强度(σs)和伸长率(δ)分别比熔铸态合金提高38HRA、115.7MPa、29.8MPa和3.8%。

添加Si和Al的Cu-9Ni-2.5Sn合金的热处理工艺

对同时添加Si和Al的Cu 9Ni 2 5Sn合金进行了热处理工艺试验。通过金相、透射电镜观察其组织 ,并对其硬度、电导率进行了测量。分析结果表明 ,经添加Si和Al的Cu 9Ni 2 5Sn合金宜采用热轧 (96 0℃～ 70 0℃ )空冷 +冷轧 (变形量 90 % ) +时效 (480℃ )的热处理工艺。经此工艺处理后 ,合金在保持硬度不变的同时 ,其电导率显著提高。

V对Cu-7.5Ni-5Sn合金组织和性能影响

用高频感应熔炼炉制备3种不同V含量的Cu-7.5Ni-5Sn合金,经均匀化、固溶和时效处理后,测试试样硬度和导电率,研究添加V对合金显微组织和合金性能的影响。研究表明,添加V会细化合金组织,并抑制时效过程中晶界不连续沉淀的产生,而且随V含量的增加,对晶界沉淀抑制作用增强。Cu-7.5Ni-5Sn在380℃时效5 h获得峰值硬度274.6 HV,而Cu-7.5Ni-5Sn-0.2V和Cu-7.5Ni-5Sn-0.5V峰值硬度均在时效7 h后获得,分别为276 HV和289 HV,这是因为V与Ni生成Ni3V共格沉淀相,因此加V合金硬度高。添加V会延长合金硬化峰值的时效时间,同时增强硬化效果。

Effect of Si and Ti on dynamic recrystallization of high-performance Cu-15Ni-8Sn alloy during hot deformation

Effect of Si and Ti on dynamic recrystallization(DRX)of Cu-15Ni-8 Sn alloy was studied using hot compression tests over deformation temperature range of 750-950℃and strain rate range of 0.001-10 s^-1.The results show that the dynamic recrystallization behavior during hot deformation is significantly affected by the trace elements of Si and Ti.The addition of Si and Ti promotes the formation of Ni16Si7Ti6 particles during hot deformation,which promotes the nucleation of dynamic recrystallization by accelerating the transition from low-angle boundaries(LABs)to high-angle boundaries(HABs).Ni16Si7Ti6 particles further inhibit the growth of recrystallized grains through the pinning effect.Based on the dynamic recrystallization behavior,a processing map of the alloy is built up to obtain the optimal processing parameters.Guided by the processing map,a hot-extruded Cu-15 Ni-8Sn alloy with a fine-grained microstructure is obtained,which shows excellent elongation of 30%and ultimate tensile strength of 910 MPa.

Wear map for sliding wear behavior of Cu-15Ni-8Sn alloy against bearing steel under oil-lubricated condition

Wear behaviors of a peak-aged Cu-15Ni-8Sn alloy fabricated by powder metallurgy were investigated.The results indicated that the friction coefficients and the wear rates of Cu-15Ni-8Sn alloy within a normal load range of 50−700 N and a sliding speed range of 0.05−2.58 m/s were less than 0.14 and 2.8×10−6 mm3/mm,respectively.Stribeck-like curve and wear map were developed to describe the oil-lubrication mechanism and wear behavior.The equation of the dividing line between zones of safe and unsafe wear life was determined.Lubricating oil was squeezed into micro-cracks under severe wear conditions.In addition,the lubricating oil reacted with Cu-15Ni-8Sn alloy to generate the corresponding sulfides,which hindered the repair of micro-cracks,promoted cracks growth,and led to delamination.This work has established guidelines for the application of the Cu-15Ni-8Sn alloy under oil-lubricated conditions through developing wear map.

Ageing behavior of Cu-15Ni-8Sn alloy prepared by mechanical alloying

The ageing behavior of the mechanically alloyed Cu-15Ni-8Sn alloy has been studied. Compared with the alloys prepared by casting and rapid solidification, the modulation structure developed during ageing process of those prepared by mechanical alloying is finer and much more uniform, which leads to a higher peak hardness. However, their spinodal decomposition temperature are almost the same. Cold deformation prior to ageing not only accelerates the ageing process but also increases the peak hardness of the alloy.

Effect of applied load on transition behavior of wear mechanism in Cu-15Ni-8Sn alloy under oil lubrication

Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly from 1.7×10^(-7) to 9.8× 10^(-7) mm^3/mm under the load lower than 300 N, and then increased dramatically to the climax of 216×10^(-7) mm^3/mm under the load over 300 N, which indicated the transition of wear mechanism with the increase of applied load. The wear mechanism mainly was plastic deformation and abrasive wear under the load less than 300 N. As the applied load was more than 300 N, the wear mechanism of Cu-15Ni-8Sn alloy primarily was delamination wear. Besides, the transition can also be confirmed from the different morphologies of worn surface, subsurface and wear debris. It is distinctly indicated that the appearance of flaky debris at the applied load over 300 N may be a critical point for the change of wear mechanism.

Microstructures of spinodal phases in Cu-15Ni-8Sn alloy

The microstructures of spinodal phases in Cu-15Ni-8Sn alloy were studied by TEM. It was found that when the alloy is completely in a as-quenched state, spinodal decomposition is quick. Ordering appears after spinodal decomposition. The ordered phase with DO22 structure has three variants obtained from coarsening spinodal structure. The reason of ordering appeared after spinodal decomposition is that the content of solute atoms needed by ordering is higher than the average, which can be reached by the composition fluctuation of spinodal decomposition. It was speculated that the morphology of the ordered phase is needle-like.

Effects of nanoscale Sn segregation on corrosion behavior of laser powder bed fusion Cu-15Ni-8Sn alloy

Corrosion resistance of laser powder bed fusion(LPBF)Cu-15Ni-8Sn alloys is crucial towards its practical application in marine engineering.In this work,corrosion behavior of LPBF Cu-15Ni-8Sn alloy was com-prehensively investigated.The results suggest that LPBF Cu-15Ni-8Sn alloy exhibits superior corrosion re-sistance than the conventional casting counterpart and their corrosion behavior is highly associated with Sn segregation.Generally,a triple-layer film will be formed on the surface of LPBF Cu-15Ni-8Sn alloy when being exposed to 3.5 wt%NaCl solution.To be more detailed,the abundance of nanoscale Sn-rich precipitates at the molten pool boundaries promotes the initial formation of a thick inner layer,where Ni and Sn tend to be distributed at inner and outer positions of the layer,respectively.In contrast,the inner layer on molten pools is much thinner ascribed to a lower Sn content,facilitating the earlier nucleation and growth of a compact middle layer that is mainly composed of numerous Cu-rich nanoparticles.At the outmost position,CuO,Cu(OH)_(2) and Ni(OH)_(2) constitute the major composition of the loose layer.The results of this study could contribute to the optimal design and processing of additively manufactured Cu-Ni-Sn alloys.

Effect of solidification rate on dendrite segregation and mechanical properties of Cu-15Ni-8Sn alloy prepared by directional solidification

The microstructures and mechanical properties of the directionally solidified Cu-15Ni-8Sn alloy were investigated at solidification rates ranging from 100 to 3000μm/s.The results showed that the solidification rate significantly affects the phase distribution of the as-cast Cu-15Ni-8Sn alloy.The primary and secondary dendritic spacing reduces and eventually becomes stable as the solidification rate increases.Meanwhile,the size of the primary phase decreases,and its distribution becomes more uniform.The most severe segregation problem of this alloy has been greatly improved.Upon solidification at 100μm/s,the as-cast Cu-15Ni-8Sn alloy consists of the α-Cu matrix,γ-CuNi_(2)Sn phase,discontinuous precipitation structure,modulated structure,and DO_(22) ordered phases.However,as the solidification rate increases,the discontinuous precipitation structure,modulated structures,and DO_(22) ordered phases decrease and even disappear,reducing hardness.As the solidification rate increases,after homogenization treatment,the composition and microhardness distributions of Cu-15Ni-8Sn alloy become more uniform.The time for homogenization is also shortened.It reduces production energy usage and facilitates further mechanical processing.