复压复烧对烧结减摩Cu-Ti3SiC2导电材料性能的影响

利用粉末冶金技术制备了10%Ti3SiC2颗粒增强Cu基减摩、导电材料。以200,400和500 MPa的压力对烧结试样进行复压,然后复烧,以提高材料的密度。通过测量试样的密度、硬度和电阻率,探索了复压复烧对材料性能的影响,并对试样进行了通电和不通电情况下的摩擦、磨损试验。结果表明,经400 MPa复压复烧后,材料的密度和硬度得到显著提高,密度由7.309 g·cm-3增加至7.712 g·cm-3,而硬度则达到HB 114,导电性能和减摩、抗磨能力也因此得到了改善,摩擦系数有所降低,磨损量减少了68%。与未带电的情况相比,带电时的摩擦因数相对较小,但磨损量则较大。在带电磨损实验过程中,摩擦副的温度升高使样品表面的铜基体部分氧化,并起到了润滑作用,从而降低了摩擦因数。     

美国的Ancordense新工艺

美国 Riverton的Hoeganaes公司开发出一种新的Ancordense工艺,它是粉末冶金零件致密化的最重大进展之一。这一新工艺只通过一次压制便可生产出低成本的铁基粉末冶金零件,而且性能优良(高拉伸强度、屈眼强度、延伸率、冲击性能及疲劳强度等)。密度可达到7.2～7.6g/cm~3,这是复压/复烧或渗铜工艺所能达到的密度,而生产成本却要比复压/复烧或渗铜工艺低得多,甚至可与粉末锻造相竞争。     

工艺参数对复压复烧铁基耐磨材料密度的影响

本文研究了初压压力、初烧温度对复压密度和复烧密度的影响。     

冷压烧结法制备Al2O3/Cu复合材料

采用压坯烧结加复压复烧工艺制备出A12O3／Cu复合材料。Al2O3颗粒的尺寸分别为2μm、7μm、10μm，体积含量分别为5％、10％、15％。结果表明，一次烧结工艺是影响材料密度的关键因素；复压及复烧能够进一步提高复合材料的密度及性能。金相组织观察表明，Al2O3颗粒分布均匀，与基体的界面结合良好。     

Cu_3P对复压复烧Fe-2Ni-1Cu-0.6C合金组织与性能的影响

采用复压复烧法制备粉末冶金Fe-2Ni-1Cu-0.6C合金。考察Cu3P添加剂对合金组织和性能的影响,并通过调节预烧温度进行预烧工艺优化。结果表明:由于Cu3P对Fe-2Ni-1Cu-0.6C复压复烧合金具有促进烧结,使珠光体组织均匀化,产生较强的固溶强化等几个方面的作用,少量Cu3P的加入可提高合金的抗弯强度和硬度;预烧温度的优化能有效控制Cu3P添加导致的合金复压复烧密度和冲击韧性的降低,从而使含Cu3P合金的性能得到进一步提高。其中,720℃预烧-复压复烧的Fe-2Ni-0.5Cu-0.58Cu3P-0.6C合金的抗弯强度和硬度达到最大值,分别为1 354 MPa和85.5 HRB,其冲击韧度为8.61J·cm-2。     

铝镇静钢渗碳时奥氏体晶粒尺寸的控制

《Transactions of ISIJ》1988年№8报导:由于铝镇静钢的渗碳温度有时在临介点以上,同临介间温度处理不同,此时奥氏体晶粒会广泛地长大。因此,必须采取措施以控制奥氏体晶粒尺寸。为使铝镇静钢在渗碳后仍维持细晶组织而不致发生反常的晶粒长大,可采取以下三种措施(这些措施都是藉助于细小均匀的AIN 沉淀粒子对奥氏体晶粒长大的抑制作     

高密度铁基粉末冶金零件制备技术

介绍了东睦新材料集团股份有限公司已经使用的高密度铁基粉末冶金产品制造技术,包括温压成形、温模压制、复压复烧等,并讨论了这些技术的优缺点。所述高密度铁基粉末冶金零件制备技术虽可以提升粉末冶金零件的密度,强度也达到较高的水平,但是零件的精度及粗糙度等尚不能满足高端应用的要求,仍需进一步机加工。未来仍需提升粉末冶金模具的制造精度、粉末特性和工艺稳定性,开发低成本、高精度、高强度的烧结铁基零件制备技术。     

高温渗碳齿轮钢铝氮含量对奥氏体尺寸的影响

 轨道交通用高端齿轮钢往往要求长时间高温渗碳处理以提高其表面硬度与耐磨性,利用合适的铝、氮含量实现AlN粒子对奥氏体晶界的有效钉扎对保证齿轮的晶粒度、力学性能与尺寸精度至关重要。在通常的渗碳温度下,AlN已经发生了部分固溶,为了保证高温渗碳后奥氏体晶粒细小,齿轮钢中的酸溶铝质量分数一般需要保持在0.02%~0.055%以保证析出足量细小的AlN第二相粒子来钉扎晶界,且氮质量分数要求为0.01%~0.016%。这一元素含量范围较广,因此有必要研究钢在高温渗碳时所需要的恰当铝氮积与铝氮比,也就是钢中w(Al)与w(N)的乘积和比值的取值范围,还需要研究AlN粒子对于奥氏体的钉扎作用。针对不同含铝含氮轨道交通用齿轮钢进行了伪渗碳试验与AlN第二相粒子Ostwald熟化和Gladman钉扎模型计算研究,揭示了奥氏体晶粒不均匀性因子Z与加热温度T的定量关系式。研究了含铝含氮齿轮钢高温保温过程奥氏体晶粒半径R_A的变化规律,以及不同铝氮积和铝氮比对奥氏体晶粒生长的影响。结果表明,加热温度T在1 173~1 273 K范围内,此类微合金高强钢的奥氏体晶粒长大不均匀性因子服从线性规律Z=3.742 97-0.001 76T;保温时间t一定时,lnR_A与1/T大致呈二次多项式关系;加热温度T一定时,lnR_A与lnt呈线性关系,奥氏体生长时间指数为0.33;当钢中铝氮积大于4.77×10-4、对应奥氏体晶粒粗化温度T_C>1 263 K时,在T=T_C-10 K温度下保温6 h后,铝氮比为1.5~3.8的钢均可保证其奥氏体晶粒度达到7级以上;当铝氮积或T_C为定值时,同样在T=T_C-10 K加热温度下保温6 h后,钢的奥氏体晶粒大小与其铝氮比呈线性正相关;铝氮比在1.5~3.8范围内,其奥氏体晶粒度相差约在1级以内。     

超细金属粉末注射成形在聚变装置钨零部件中的应用

从超细粉末制备、喂料准备、注射工艺、烧结工艺和热等静压处理等方面研究了超细纯钨粉以及超细稀土氧化物弥散增强钨粉的金属注射成形技术,利用该技术制备了聚变装置中的钨零部件,并对这种超细金属粉末注射成形钨零件的微观组织和热力学性能进行了分析。结果表明:超细纯钨粉零件相对密度可达98%以上,平均晶粒尺寸10~15 μm,500℃以上的热导率与锻造钨零件相当;超细稀土氧化物弥散增强钨粉零件相对密度可达99%以上,平均晶粒尺寸3~5 μm,抗热冲击性能优良。     

复压复烧对Ni-20Cr/hBN自润滑复合材料力学性能及摩擦磨损性能的影响

采用粉末冶金法制备Ni-20Cr/hBN复合材料,研究300 MPa复压8 s,1 150℃复烧2 h对该材料力学性能和摩擦磨损性能的影响。结果表明,当hBN含量为10%时(质量分数),复压复烧1次可使密度由5.35 g/cm3提高至5.5 g/cm3,孔隙率由19.87%降低至16.67%,抗弯强度由75.03 MPa提高至115.11 MPa,硬度由19.46 HB提高至20.12 HB。多次复压复烧对Ni-20Cr/hBN复合材料性能影响较小。hBN含量为10%时Ni-20Cr/hBN复合材料在室温、400℃和600℃下的摩擦因数分别为0.808、0.898和0.914,质量磨损分别为63.7、141.5和204.4mg/min,经过1次复压复烧之后摩擦因数分别降低21.78%、25.72%和26.15%,磨损率分别降低32.16%、54.55%和50.70%。     

A model to predict carburization profiles in high temperature alloys

A mathematical model has been developed which, by means of finite difference computation techniques, permits the prediction of carbon concentration profiles in carburized high temperature alloys. It is assumed that a proportion of the carbon which diffuses into the alloy reacts with elements such as chromium to form carbide precipitates. The amount of carbon remaining in solution is determined from the solubility product of the carbide. Only this carbon in solution is able to diffuse through the alloy matrix, and thus the carbide precipitation process reduces the rate of carburization. Applying the model, the diffusion coefficient of carbon in Alloy 800 H at 900 °C has been determined as (3.3 ± 0.5) × 10⁻⁸ cm²/s. The model can also treat the carburization of an alloy containing two carbide-forming elements, but application to alloys containing both chromium and niobium (columbium) was successful only to a limited extent, probably as a result of the slow, complex kinetics of carbide precipitation. The model can be used to adapt carbon concentration profiles from one geometrical configuration to another. On the basis of profiles determined experimentally on small, cylindrical test specimens, carbon concenration profiles have been predicted for thick section tubes of Alloy 800 H exposed to a carburizing environment for up to 100,000 h. Formerly of the Institute of Reactor Materials, Nuclear Research Centre (KFA), Jülich     

不同渗碳层深度下重载齿轮钢的疲劳性能

 国家工程研究中心, 北京100081;3. 中国钢研科技集团有限公司科技质量部, 北京 100081)     

Effect of surface carburization on dynamic deformation and fracture of tungsten heavy alloys

Effects of surface carburization on dynamic deformation and fracture behavior of tungsten heavy alloys were investigated in order to improve the penetration performance. Dynamic torsional tests using a torsional Kolsky bar were conducted on four specimens, three of which were carburized by the case carburization process. The test data were then compared with hardness, Charpy impact energy, adiabatic shear banding, deformation and fracture mode, and penetration performance. With increasing carburization temperature and time, surface hardness increased, but impact energy decreased. The dynamic torsional test results indicated that for the carburized tungsten specimens, cleavage fracture occurred in the center of the gage section with little shear deformation, whereas shear deformation was concentrated at the center of the gage section for the conventionally processed specimen without carburization. The deformation and fracture behavior of the carburized specimens correlated well with the observation of the impacted penetrator specimens, i.e., microcrack initiation at tungsten particles and cleavage crack propagation. Since the cleavage fracture mode is thought to be beneficial for self-sharpening, these findings suggest the beneficial effect of the surface carburization on the penetration performance.     

通过等离子渗碳/CrN覆层改性处理提高Ti-6Al-4V合金的耐磨性和抗疲劳特性

In this study, a newly developed duplex coating method incorporating plasma carhurization and CrN coating was applied to Ti-6AI-4V and its effects on the wear resistance and fatigue life were investigated. The carburized layer with approximately150μm in depth and CrN coating film with 7. 5 μm in thickness were fomled after duplex coating. Hard carbide particles such as TiC And V4C3 were formed in the carburized layer. XRD diffraction pattern analysis revealed that CrN film had predominant [111] and [200] textures. The hardness (Hv) was significantly improved up to ahout 1960 after duplex coating while the hardness value of original Ti-6Al-4V was 402. The threshold load for the modification and/or failure of CrN coating was measured to be 32 N using the acoustic emission technique. The wear resistance and fatigue life of duplex coated Ti-6Al-4V improved significantly compared to those of un-treated specimen. The enhanced wear resistance can be attributed to the excellent adhesion and improved hardness of CrN coating film for the duplex coated Ti-6Al-4V. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the surface, resulting in the enhanced fatigue life.     

铈与YG6硬质合金制备过程中富钙相的交互作用

在硬质合金的原材料仲钨酸铵(APT)粉末中添加Ca和稀土Ce元素,探讨稀土Ce元素与硬质合金制备过程中富钙相的交互作用。材料的物相组成、显微结构及成分分别通过X射线衍射仪、扫描电子显微镜及能谱进行检测与分析。结果表明:氧化钨还原过程中会产生CaWO_4和Ca_(4.26)W_(10)O_(30)两种富钙相,分布在钨颗粒内部和周围,使钨颗粒的棱角钝化,碳化后富钙相转变为Ca_(4.26)W_(10)O_(30)和CaC_2相,富钙相可急剧降低YG6硬质合金的性能;添加适量稀土Ce可降低富钙相对钨粉的影响,钨粉颗粒的棱角变得明显,颗粒尺寸变小且分布均匀,稀土Ce与富钙相发生反应生成Ce_(0.9)Ca_(0.1)O_(1.9)三元相;稀土Ce与富钙相的交互作用效果显著,与1%Ca-YG6硬质合金相比,1%Ce+1%Ca-YG6硬质合金的致密度、硬度和断裂韧性分别提高了7.8%,34.3%和67.8%。     

Vacuum carburization of 12Cr2Ni4A low carbon alloy steel with lanthanum and cerium ion implantation

As bearing parts, 12 Cr2 Ni4 A is expected to have high hardness and excellent fatigue strength, so carburizing is employed to improve the inherit properties of 12 Cr2 Ni4 A. However, the traditional carburizing is limited by poor microstructure distribution and low rate of carburizing. The rare earth ion implantation is known to help improving the properties of tribology, corrosion resistance and oxidation resistance of metal. In this article, the RE implantation is employed to assist the carburizing. Lanthanum and cerium ion implantations are initially used to assist 12 Cr2 Ni4 A low pressure vacuum carburization.The microstructure, content of retained austenite, hardness, thickness of layer and carbon diffusion were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD) and Rockwell/Vickers hardness tester, respectively. It was shown that lanthanum and cerium implantations can improve structure of the vacuum carburizing layer, and enhance the uniformity of carbon element distribution on the carburized surface. Meanwhile the RE implantation plays a positive role in promoting the surface hardness and carburized rate. The lanthanum element has more significant effect on surface hardness and content of retained austenite than cerium element. The surface hardness of lanthanum element implanted layer was 62.9 HRC with 9.6% content of retained austenite, while the carburizing rate of cerium implanted layer increased by 12.4%.     

高温渗碳齿轮钢的研究进展

常用齿轮钢渗碳温度为930℃,提高渗碳温度至1000～1050℃能显著缩短渗碳时间,但易引起晶粒长人,因此发展了通过Nb、Ti、B微合金化,细化钢原奥氏体晶粒的高温渗碳齿轮钢。文中介绍了国内外高温渗碳齿轮钢的钢种成分、工艺特点、高温渗碳层组织控制和钢的疲劳性能的研究进展。     

Application of secondary ion mass spectrometry to the study of carburization of superalloy

Secondary ion analysis was applied to the study of the carburization behavior of a superalloy by using the ion microprobe mass analyzer (IMMA). The corrosion test of Inconel 617 was carried out for 1000 h under an environment of methane-doped impure helium gas at 1000 °C. 20 KeV O ₂ ⁺ and N ₂ ⁺ were used as primary ions. IMMA showed that C, O, Al, Si, Ti and Mo were enriched near the surface. The chemical states of the scale and the precipitates were determined from chemical shifts of X-ray emission spectra. It was confirmed that silicon carbide and molybdenum carbide were coprecipitated in the same areas: in the scale, in the matrix at a depth of 10 μm to about 40 μm below the scale, and at grain boundaries. Aluminum and titanium were found to exist as oxides near the surface. It was shown that carburization was limited near the surface, and the grain boundary precipitation of carbides in the bulk was due to aging at high temperatures. The concentration profiles of silicon and molybdenum in (Si,Mo)-carbide were obtained by using standard carbide samples assuming that the concentration of implanted oxygen atoms of the specimen was equal to that of the standard sample. The ratio, (Si)/(Mo), was increased from about 0.1 in bulk to 2.4 ∼ 3.8 near the surface. This result indicates that silicon is carburized much more preferentially than molybdenum.     

Microstructure and Mechanical Properties of Gear Steels After High Temperature Carburization

High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity. However, the commonly used gear steels which are microalloyed by Al are not suitable for high temperature carburization due to abnormal grain coarsening. The gear steel 20CrMnTiNb, which is microalloyed with 0. 048% Nb and 0. 038% Ti, has been compared with the gear steel 20CrMn in terms of microstructure in the case of hardened layer and in the core after carburizing at 1000 °C for 4 h and mechanical properties after carburizing and pseudo-carburizing. The results indicate that the fine austenite grains exist in the carburized case of 20CrMnTiNb steel, while there is abnormal coarsening and duplex grain structure in the case and core of steel 20CrMn. The average prior austenite grain sizes are 19.5 and 34.2 μm for the steels 20CrMnTiNb and 20CrMn, respectively. In addition, the mechanical properties of 20CrMnTiNb steel are superior to those of 20CrMn steel. In particular, the HV hardness of the former is higher than that of the latter by about 40–70 in the range of less than 0.7 mm in depth. Therefore, the steel 20CrMnTiNb is suitable for high temperature carburization.