退火热处理对Cr_(3)C_(2)-FeCrBSi涂层摩擦磨损性能的影响

Effect of Annealing Treatment on Friction and Wear Properties of Cr_(3)C_(2)-FeCrBSi Coatings

目的 针对冷轧辊表面的循环应力、摩擦磨损的特殊服役环境,设计空气燃料超音速火焰喷涂(HVAF)制备Cr_(3)C_(2)-FeCrBSi复合涂层来提高工件表面的硬度和耐磨性。方法 利用HVAF技术在冷轧辊用合金钢板表面制备不同尺寸陶瓷颗粒混合的Cr_(3)C_(2)-Fe CrBSi的复合涂层,并在600、700、800℃进行退火处理后得到退火态涂层。利用XRD、SEM、显微硬度计、电子拉伸试验机、盘式摩擦磨损试验机和接触疲劳试验机,考察了不同陶瓷含量和不同退火温度下涂层的相组成、组织结构、机械性能、摩擦磨损性能和接触疲劳失效形式。结果 喷涂态涂层的显微硬度、结合强度随着Cr_(3)C_(2)含量的增加先上升后下降。当陶瓷相质量分数为10%时,复合涂层最佳,显微硬度、结合强度分别为459.6HV0.3、42.8 MPa。选取Cr_(3)C_(2)(质量分数10%)-FeCrBSi涂层经过退火处理后,涂层的硬度、断裂韧性、抗磨损性能均有提升,其中摩擦因数由原先的0.89降低至0.80~0.75。此外在700℃下退火3 h得到的涂层,显微硬度可达490.3HV0.3,断裂韧性由2.81 MPa·m1/2提升至3.15 MPa·m1/2,磨损率为6.80×10^(-14) m^(3)/(N·m),与喷涂态涂层相比,磨损率降低了15%。喷涂态、退火态涂层的磨损机制均为磨粒磨损。接触疲劳试验结果表明,退火态复合涂层的接触疲劳失效形式主要有剥落和分层,同时剥落失效情况下涂层的接触疲劳寿命更长,可达2.07×10^(5)转。结论 Cr_(3)C_(2)-Fe Cr BSi复合涂层良好的抗磨损和耐接触疲劳性能主要取决于Cr_(3)C_(2)硬质耐磨颗粒的加入。而退火热处理可以促进涂层向平衡态的转变、同时析出的二次碳化物(Cr, Fe)7C3起到沉淀强化的作用,使得退火态涂层具有更好的抗摩擦磨损性能。

High Velocity Air Fuel(HVAF)technology is a coating preparation method with operating temperature between the range for High Velocity Oxygen Fuel(HVOF)technology and Cold Spray(CS)technology.Therefore,it can reduce the thermal effect on the spray particles while ensuring their fully melted.Cermet prepared by thermal spraying is usually used for surface protection of parts because of its advantages of high hardness and good bonding strength.However,HVOF technology will lead to the inevitable decomposition of ceramic phase and affect the quality of coating.Therefore,the work aims to use the HVAF technology with lower calorific value to prepare Cr_(3)C_(2)-FeCrBSi according to the background of cold roller protection for a series of characterization.Considering the particle size,the content of ceramic powder and the effect of annealing on coating properties,micron and submicron Cr_(3)C_(2) powders were added into FeCrBSi to prepare coatings with different ceramic contents.The wear resistance of composite coatings before and after annealing was studied.The D2 alloy steel was cut into 100 mm×30 mm×6 mm rectangular blocks andϕ25 mm×55 mm cylindrical blocks.Cr_(3)C_(2)(Micron:Submicron=1∶1)in different ratios(5wt.%,10wt.%,15wt.%)was added to FeCrBSi as the reinforcing phase.The Cr_(3)C_(2)-FeCrBSi coating was prepared by mechanically mixing the metal and ceramic particles using HVAF on the substrate.The surface and cross-section of the samples were polished after they were cut into 15 mm×15 mm×6 mm blocks by wire cutter.Then,the microscopic morphology and elemental distribution were analyzed by scanning electron microscope(SEM)and Energy Dispersive Spectrometer(EDS).The porosity was measured through a 500×magnification of the cross-section.The phase composition was analyzed with X-ray energy dispersive spectrometer(XRD).The microhardness was measured with a microhardness tester and the fracture toughness was calculated by equation.The bond strength was tested by tensile method.The three-dimensional wear morphology and wear volume of the coating were measured by probe contact profiler.Finally,the coating with the best ceramic content was annealed at 600℃,700℃,and 800℃ for 3 h,and then the characterization methods were repeated to determine the effect of annealing treatment on friction and wear properties.The microhardness and bond strength of the coating increased firstly and then decreased with the increase of Cr_(3)C_(2) content.When the ceramic phase content was 10wt.%,the microhardness and bond strength were 459.6HV0.3 and 42.8 MPa,respectively.The microhardness,fracture toughness and abrasion resistance of Cr_(3)C_(2)(10wt.%)-FeCrBSi coating were improved after annealing.The average coefficient was reduced from 0.89 to 0.80-0.75.After annealing at 700℃ for 3 h,the microhardness reached 490.3HV0.3,the fracture toughness increased from 2.81 MPa·m1/2 to 3.15 MPa·m1/2,and the wear rate was 6.80×10^(‒14) m^(3)/(N·m).Compared with as-sprayed coating,the wear rate was reduced by 15%.The wear mechanism was abrasive wear.At the same time,the contact fatigue life of the coating was longer under the condition of peeling failure,which could reach 2.07×105 revolutions.Annealing treatment could improve the stress and defects of Cr_(3)C_(2)-FeCrBSi coating and improve the overall performance.After annealing at 700℃ for 3 h,the secondary carbides in the coating were precipitated and the pores shrank,which made the coating show the best friction and wear properties.In addition,the contact fatigue failure of composite coatings takes the form of spalling and delamination.