Preparation Of A Cu-Ni Alloy Aiming At Low Temperature High Ductility And Research Of Its Organization And Properties

Wear-resistant copper alloys are widely used to produce gears,bearings,seals,hydraulic pump friction pairs owing to their excellent wear resistance and corrosion resistance as well as acceptable mechanical property.The traditional wear-resistant copper alloys mainly include brass,aluminum bronze and tin bronze.Meanwhile,sometimes,Cu-Ni cupronickel alloys are also used to make some high-strength wear-resistant parts.With the rapid development of modern aerospace fields,it is required that the wear-resistant copper alloys have good comprehensive mechanical properties(especially high impact toughness)under low temperature environmental conditions.According to an earlier compilation from literatures and our investigation,among all the copper alloys,the hot-worked Cu-Ni alloys have relatively higher impact energies(more than 100J)at low temperatures with a considerable mechanical strength.However,the low-temperature impact toughness of copper-nickel alloys hasn't been publicly reported in our country yet.Furthermore,the value of the impact energy depends on the preparing processes and the hot-deformed Cu-Ni alloys show great potential of high impact toughness.Thus,it's crucial to develop a hot-deformed Cu-Ni alloy for the low temperature application fields in aerospace.In order to solve these problems,the hot deformation behavior of coper-nickel alloy is investigated by compression test with gleeble-1500 thermal simulator.The processing maps and constitutive equation for hot deformation are established based on the experimental stress-strain data at different temperatures and strain rates.The hot deformation activation energy Q for the alloy is determined to be 327.128 kJ/mol.The processing maps for the alloy obtained at strain of 0.7 reveals a region of dynamic recrystallization existing in the temperature range of 830?950? and strain,rate of 0.01?0.056 s-1,with a peak efficiency about 39%.The optimum parameters for hot deformation of the alloy are around 900? at strain rates of 0.01?0.056 s-1,which can be obtained from the processing map.In addition,the maps exhibit two wide domains of flow instability:(1)700?760? with 0.032?0.25 s-1 and(2)760?950? with 0.32?10 s-1.According to the processing map,a hot forged Cu-Ni30-Fe-Mn-Zn alloy was prepared.The specimen was kept at 1050 ? for 4h,and then the alloy ingot was proceed with three upsetting and three pulling process,the strain rate is Is-1.The impact energy for the hot forged alloy is up to 262J at liquid nitrogen temperature,which shows great prospects in the low temperature fields.At the same time,the ultimate tensile strength are 395MPa and 575MPa at room temperature and cryogenic temperature,respectively.After solution treated at 900? for 2h,the grains grow up.And the strength,plasticity,hardness and impact toughness of the alloy were reduced.After aging treatment,the performance of the alloy is similar to that of the solution treated alloy.And the aging time and temperature have little effect on the properties of the material.The grain size and the lattice constant of Cu-Ni30-Fe-Mn-Zn alloy become smaller after a deep cryogenic treatment in liquid nitrogen and the hardness value is slightly improved.The alloy has good dimensional stability at low temperature.Cu-Ni30-Fe-Mn-Zn alloy in the case of dry friction,the friction coefficient is 0.74 and the weaing mechanism is serious adhesive wear with plastic deformation and flake off;the friction coefficient dropped to 0.12 after adding MoS2 lubricant,which indicates that the lubricant has a good lubrication,the weaing mechanism is slight adhesive wear and the morphology of Cu-Ni30-Fe-Mn-Zn alloy becomes narrower and shallow.But compared with other wear-resistant copper alloy commonly used in low temperature,the wear resistance of Cu-Ni30-Fe-Mn-Zn alloy is poor and it will take place serious adhesive wear.