含纳米颗粒的铁基粉末冶金件直接渗碳工艺研究

在铁基粉末中分别添加纳米Fe和Cu颗粒混合，并对其粉末冶金件烧结时直接渗碳和烧结后渗碳的工艺进行实验研究，结果表明：直接渗碳的试样，在密度、表面硬度和有效硬化层硬度值均高于烧结后再进行渗碳试样的各项指标数据。     

深层渗碳对H13钢显微组织和硬度的影响北大核心CSCD

采用OM、TEM和XRD对深层渗碳处理后H13钢的显微组织进行观测,研究了深层渗碳对H13钢显微组织和硬度的影响。结果表明:渗碳后完全退火试样与渗碳后球化退火试样的渗碳层厚度均在3 mm以上,组织细密均匀,硬度提高30%~60%;渗碳后球化退火试样的晶粒更细小,基体上碳化物弥散分布并存在较多的亚结构,且表面硬度稍高于渗碳后完全退火试样。最佳深层渗碳处理工艺为1000℃下固体渗碳4 h,接着进行球化退火(840℃保温4 h,炉冷到740℃再保温4 h,炉冷到500℃后空冷到室温),然后进行1030℃淬火10 min,最后进行560℃回火2次,每次2 h。     

深层渗碳对H13钢显微组织和硬度的影响

采用OM、TEM和XRD对深层渗碳处理后H13钢的显微组织进行观测,研究了深层渗碳对H13钢显微组织和硬度的影响。结果表明:渗碳后完全退火试样与渗碳后球化退火试样的渗碳层厚度均在3 mm以上,组织细密均匀,硬度提高30%~60%;渗碳后球化退火试样的晶粒更细小,基体上碳化物弥散分布并存在较多的亚结构,且表面硬度稍高于渗碳后完全退火试样。最佳深层渗碳处理工艺为1000℃下固体渗碳4 h,接着进行球化退火(840℃保温4 h,炉冷到740℃再保温4 h,炉冷到500℃后空冷到室温),然后进行1030℃淬火10 min,最后进行560℃回火2次,每次2 h。     

真空渗碳均匀性测试

测定了30CrMnTi钢试样在卧式双室真空渗碳炉渗碳并炉冷或淬火后的渗碳层深度、有效硬化层深度和表面硬度的均匀性。结果表明,按目标渗层深度1.0 mm真空渗碳和炉冷的试样,用金相法测定的渗层深度偏差≤0.10 mm。按目标渗层深度1～2 mm真空渗碳和淬火的试样的有效硬化层深度偏差≤0.10 mm。同炉次渗碳、淬火试样的表面硬度偏差≤1.5 HRC,不同炉次渗碳、淬火试样的表面硬度偏差≤2.5 HRC。     

重载汽车20CrMnMo齿轮激光淬火热处理工艺

为研究20CrMnMo齿轮经激光淬火后的硬度值和微观组织以及与其他热处理方式相比的差异,采用"渗碳淬火"和"渗碳后不同参数的激光淬火"等工艺方法处理了一批齿轮;测定其齿面硬度值并对数据进行Matlab软件分析;采用扫描电子显微镜(SEM)对典型试样进行显微组织观察;测定和分析部分试样的晶粒度。结果表明:"渗碳后激光淬火"齿面的硬度值最高可达61.4 HRC,比渗碳淬火齿轮高2.3 HRC左右;渗碳后激光淬火的高硬度值试样的微观组织为致密的针状马氏体与板条状马氏体的混合,晶粒度为9级左右,有熔融现象的试样微观组织为回火索氏体,且不同激光参数处理的试样其微观组织类型和尺寸差别较大。因此20CrMnMo齿轮可以通过渗碳后的激光淬火工艺获得较高的硬度值、较好的微观组织和晶粒度。     

Q235钢在溶液中微弧渗碳过程的研究

探讨了Q235钢在溶液中快速微弧渗碳过程。通过观察渗碳过程、渗碳金相组织,借助SEM观测渗碳层形态,利用显微硬度计测试表面硬度,初步认识了溶液中快速微弧渗碳工艺的条件和过程。结果表明,在电压150 V左右,对试样微弧渗碳15 min后,试样表面化合物层的硬度能达到710 HV左右,约为基体硬度的4倍。     

高浓度渗碳及其性能研究

对比研究了高浓度渗碳与常规渗碳后试样的组织和性能。结果表明：高浓度渗碳试样的硬度，耐磨性，接触疲劳性能最高，弯曲疲劳性能与常规渗碳试样的大致相同，并对试验结果进行了较为系统的微观机理分析。     

Cr35Ni45Nb钢铝硅共渗涂层抗渗碳性能研究

对乙烯裂解炉管材料Cr35Ni45Nb钢进行铝硅共渗处理。对处理后试样进行观察分析,渗层由渗剂残留组成的粘附层、互扩散层和连续白亮的渗层组成共渗。处理后基体硬度没有变化。对未进行铝硅共渗处理的试样渗碳处理,发现试样出现约40μm渗碳层,基体分布着碳化物颗粒。而铝硅共渗处理后的试样渗碳后,碳化物颗粒均分布在渗层,渗碳层硬度约为20μm,基体内无碳化物颗粒。因此铝硅共渗处理提升了材料的抗渗碳能力。     

表面形貌对316L奥氏体不锈钢低温气体渗碳的影响

利用金相显微镜、显微硬度计和残余应力分析仪研究了4个具有不同表面形貌的316L奥氏体不锈钢经低温气体渗碳处理后的渗碳层微观形貌、硬度和残余应力。结果表明:渗碳后各试样表面均形成一层高硬度、高残余压应力的渗碳层,表面强化效果显著。表面形貌对316L奥氏体不锈钢低温气体渗碳有一定影响。随着试样表面粗糙度的下降,渗碳处理后的硬度、残余应力和渗碳层厚度均降低,表面强化效果下降,并最终趋于稳定。     

渗碳工艺对WC-Co梯度硬质合金的梯度结构和硬度的影响

对缺碳硬质合金采用渗碳处理制备梯度硬质合金,利用显微组织分析和维氏硬度测试等方法,研究渗碳工艺对梯度硬质合金的梯度结构和硬度的影响。结果表明：渗碳处理后随着渗碳时间延长,梯度层厚度增大,长时间渗碳还会出现梯度结构消失现象;渗碳时表面层WC晶粒长大,且渗碳时间越长晶粒长大越严重;渗碳后梯度硬质合金的表面硬度明显提高;渗碳后合金的表面硬度明显高于烧结态合金的表面硬度;随着渗碳时间的延长,合金表面硬度先增大后减小;合金的硬度在截面上沿梯度方向呈连续梯度变化,合金表面层因WC含量较高、钴含量较低而具有较高的硬度,中间层因钴含量较高、WC含量较低,其硬度较低。     

快速成型钼金属喷管高温烧结试验研究

结合某军品项目进行研究,对激光快速成型预烧结喷管件进行高温烧结和还原气氛二步烧结试验,测试制件的各项性能,确定此喷管件是否有进行还原气氛二步烧结的必要,并对Mo粉末高温烧结机理进行理论分析,探讨高温烧结改善坯体性能的原因.试验表明,经过还原气氛二步烧结的结构件才能达到某喷管的性能要求,还原气氛二步烧结是必要的,且高温烧结理论分析解释了这一原因.     

选择性激光烧结成形温度场的研究进展

选择性激光烧结技术与传统铸造工艺相结合,为快速制造某些难以用传统方法获得的铸件提供了有利途径.对于各种粉末材料在选择性激光烧结成形过程中温度场的模拟与预测,是合理选择其烧结工艺参数的基础.本文中综述了聚合物粉末、聚合物覆膜金属/陶瓷粉末和金属粉末在选择性激光烧结过程中的热物性参数变化规律及其相应的成形温度场分布,以利于激光选择性烧结各类粉末材料而精确成形零部件.     

Development and characterisation of direct laser sintering Cu-based metal powder

Direct laser sintering of metal powder is a promising manufacturing process to produce rapid moulds (or rapid tooling) because complex three-dimensional (3-D) metal parts can be created directly from computer-aided design (CAD) data without machining or use of additional tooling. However, material and process are still the crucial issues that restrict its wider adoption although the technology has been introduced more than 7 years. This paper characterises a self-developed Cu-based metal powder used for direct laser sintering. The material system is Cu-based alloy metal powder, which consists of two metal powders: high-purity Cu powder and pre-alloyed SCuP metal powder. The scanning electron microscope (SEM), XRD and energy dispersive X-ray (EDX) analyses show that the bonding mechanism of this process is liquid-phase sintering. The pre-alloyed SCuP metal powder with lower melting point (645 °C) acts as the binder during laser sintering, while the Cu powder with higher melting point (1083 °C) acts as the structure. The element phosphorus in the powder can act as flux to protect the Cu oxidisation. A case study on fabricating the inserts of a mobile phone cover mould was also carried out. The inserts were created in ambient atmosphere at room temperature. The total sintering time is 40 h. Sixty five percent relative theoretical density and average surface roughness R_a 14–16 μm were achieved with negligible distortion and curling. Epoxy infiltration was employed as post-process to improve the density and the strength of the sintered tooling. The mould inserts were used to inject ABS-PC mobile phone cover after polishing. No defects were found after moulding of 500 components.     

Density improvement of alumina parts produced through selective laser sintering of alumina-polyamide composite powder

A powder metallurgy (PM) process to fabricate alumina parts through indirect selective laser sintering (SLS) of spherical alumina-polyamide composite powder is presented. The PM process includes powder production, SLS, debinding and furnace sintering. Three different strategies are investigated in order to improve the density of the final alumina parts: laser remelting, warm isostatic pressing (WIP), and different infiltration techniques which use alumina containing suspensions: pressureless infiltration and infiltration under pressure (i.e. squeeze infiltration). Furthermore, microstructural and geometrical changes which occur during the PM process are investigated.     

原位内生碳化钒颗粒增强铁基表面复合材料的研究

用SEM、XRD检测浇注凝固后位于铸型表面的复合粉料压坯组织结构的变化,证实用铸造烧结技术可以在铸件表面原位生成碳化钒颗粒增强铁基表面复合材料.探讨了粉料压坯快速完成钒的碳化反应和烧结致密化的机理,用MM200磨损试验机检测了碳化钒颗粒增强铁基表面复合材料的耐磨性.     

激光微区烧结微成形技术研究

目前微小零部件的制造方法很多,激光微成形即为其中一种。介绍了在激光选区烧结技术的基础上,结合微成形特点开发的激光微区烧结成形技术。该技术可对金属粉末进行直接微区烧结成形,所成形的金属微型零件强度高,不需后续处理,大大节省了从原材料到最终实体的时间,并具有环境污染小、材料利用率高、成形速度快和效率高的特点。     

钛及钛合金粉末的注射成形

介绍了钛及钛合金粉末注射成形技术的发展、应用现状及制备工艺。指出了钛及钛合金粉末注射成形技术研究方向和扩大应用的途径是：①使用价格低廉的氢化脱氢粉和气体雾化粉混合得到的钛及钛合金粉作为注射成形的原料粉末；②开发新型高效的钛及钛合金粉末注射成形用的粘结剂体系；③优化混炼工艺；④优化注射条件参数以消除注射缺陷；⑤开发先进的脱脂工艺，使脱脂时间进一步缩短并减少脱脂缺陷，以降低成本；⑥研究钛及钛合金烧结工艺以及超小型零件的注射成形工艺，控制产品尺寸精度，提高产品性能。扩大产品的尺寸。     

Thixoforging of particle-reinforced steel materials

The paper deals with a new process chain consisting of powder metallurgy (PM) and a subsequent thixoforging process. This innovative production process can increase the complexity of PM components and enable a high formability of brittle materials such as metal matrix composites (MMC). Compared to conventional materials MMCs feature improved mechanical properties and thus a high potential for various applications. In this investigation cylindrical raw parts, consisting of a steel powder and different proportions of titanium carbide particles, were produced by uniaxial powder pressing and sintering. Subsequently, the samples were heated up to the thixotropic (semi-solid) temperature range and valve parts were thixoforged by a backwards rod extrusion process. Finally, the particle-reinforced steel parts were characterised by metallographic analysis and hardness measurements.     

The influence of powder apparent density on the density in direct laser-sintered metallic parts

In direct laser sintering, the density is expected as high as possible for the industrial application. Since the density not only determines the industrial acceptance, but also limits the accuracy of the parts. This paper reports on the influence of the powder apparent density on final density of the sintered part's in direct laser sintering of Cu-based metal powder. The relative densities of the sintered parts with the different apparent densities using different process parameters have been investigated. The result shows that the apparent density has the most significant effect on final density of the sintered part. The final density increases with the increase of the apparent density. It is easy to get a higher final density in direct laser sintering process if a higher apparent density is used. However, the final density seems to have an upper limit for a given metal powder system.