加热过程中H2O(g)含量对55SiCr弹簧钢表面氧化层及脱碳行为的影响

对55SiCr弹簧钢铸坯试样进行热重(TG)试验,研究了不同气氛下H_2O(g)含量对55SiCr弹簧钢表面氧化层及脱碳行为的影响。结果表明:混合气氛下55SiCr弹簧钢的脱碳程度高于空气下的,铁素体脱碳层厚度随混合气氛中H_2O(g)含量的增加而增大,试样在850℃时铁素体脱碳层厚度均出现峰值。与干空气相比,混合气氛下H_2O(g)的存在改变了氧化层的组成与结构,使氧化产物比重向FeO比重增加,而FeO的结构较为疏松,会使脱碳程度增加。     

黄铜表面等离子体电解氧化膜层的制备及性能分析EI北大核心

为了提高黄铜的耐蚀性能,对其表面进行等离子体电解氧化,并分析Na_(2)SiO_(3)电解质浓度对氧化膜层性能的影响。调配以Na_(2)SiO_(3)·9H 2O,NaOH为主要成分的电解液,设置正向电压为520 V、正向电流1.4 A、脉冲频率2000 Hz、正负占空比20%,对黄铜试件进行80 min的等离子体电解氧化。通过场发射扫描电子显微镜(SEM)、表面粗糙度测量仪、涡流测厚仪、能谱仪(EDS)、X射线衍射仪(XRD)、百格刀附着力测试仪、电化学工作站(动电位极化曲线),研究Na_(2)SiO_(3)浓度对氧化膜层的微观形貌、厚度、粗糙度、化学组分、结合力及耐蚀性能的影响。结果表明:膜层表面的化学组分是以Cu,Zn,O,Si等元素组成,并以金属氧化物和非晶二氧化硅的形式存在;随着Na_(2)SiO_(3)浓度的升高,膜层表面的微孔数量逐渐增多,孔洞尺寸和分布越来越均匀,膜层厚度先增大后减小,表面粗糙度值先减小后增大;然而过大的Na_(2)SiO_(3)浓度,等离子体电解氧化反应加剧,表面出现熔解现象,膜层质量不升反降。等离子体电解氧化能够有效提高黄铜的表面性能,当Na_(2)SiO_(3)浓度为8 g/L时,氧化膜层结合力和耐蚀性能最好,其自腐蚀电流密度与基体相比,下降了2个数量级。     

预氧化对1Cr11Ni2W2MoV不锈钢渗氮层质量的影响

为了研究渗氮前预氧化处理对1Cr11Ni2W2MoV材料制件渗氮层质量的影响,对调质后的试样在渗氮前进行不同预氧化处理和吹砂处理。目视观察预氧化薄膜颜色,采用金相显微镜和硬度计检测渗氮层的组织、深度、硬度和脆性等。结果表明：渗氮前对该材料在550℃下预氧化5～20 min,可以破坏不锈钢制件表面的钝化膜,使该材料制件渗层的硬度、深度及组织符合渗氮技术要求,且其渗层均匀性及渗氮速度均优于渗氮前仅进行吹砂处理的试样。     

低温低压电弧等离子体渗氮处理316不锈钢的耐腐蚀性能

在低温下对316奥氏体不锈钢进行低压电弧等离子体渗氮处理,研究了渗氮处理对不锈钢耐腐蚀性能的影响。结果表明:渗氮层有两个子层,由纳米晶扩张奥氏体和少量的Cr N化合物组成的外表层和单一结构的扩张奥氏体内层。由于低压电弧等离子体浓度高,在400℃渗氮1 h得到的渗氮层厚度达到15μm,表现出很高的渗氮速率。纳米晶外表层是渗氮不锈钢耐腐蚀性能的关键,促进了钝化膜的生成,渗氮后试样表面形成的钝化膜厚度达到27 nm,比原始不锈钢钝化膜的2倍还多。渗氮不锈钢试样的腐蚀电流(3.55×10~(-8)A/cm~2)比基材的腐蚀电流(1.99×10~(-7)A/cm~2)降低一个数量级,表明渗氮后试样的耐腐蚀性能提高了。     

SiO_2添加剂对等离子喷涂ZrO_2涂层结构和性能的影响

本文研究 SiO_2添加剂对 ZrO_2涂层结构和性能的影响。结果表明,在增加过渡层的同时,添加3wt-%左右的 SiO_2,可使涂层的粘结强度和熱冲击寿命提高4—5倍。添加剂改善涂层寿命的原因是等离子喷涂时,SiO_2熔化渗入 ZrO_2颗粒之间和孔隙中,首先起到液相烧结作用;随后在涂层内汽化(蒸发)增加其孔隙率,使涂层的应力易于松弛,而且,SiO_2以石英相形态沿平行于表面方向塞积在涂层孔隙处,隔绝氧化气氛的进入,起到“自封孔”的作用。在粘结层和 ZrO_2层之间增加过渡层,有利于涂层应力的延缓过渡。     

热处理工艺参数对13Cr11Ni2W2MoV渗氮组织及性能的影响

该文对13Cr11Ni2W2MoV不锈钢材料进行气体渗氮,用金相显微镜观察渗层氮化物组织形态,用显微硬度计检测渗层表面硬度,研究渗氮温度、渗氮时间、Kn值对渗层组织形态和表面硬度的影响。结果表明,渗氮工艺参数中,Kn值对渗层组织形态和表面硬度影响较大,当渗氮温度为600℃,Kn值降低到0.18,渗氮时间为8 h时,可获得完整、致密的渗层氮化物组织和890 HV的表面硬度,并且随着渗氮时间的延长,渗氮层厚度逐渐增加。     

高碳锰铁预氧化-真空脱碳制备低碳锰铁热力学分析及实验研究

提出高碳锰铁预氧化-真空脱碳工艺以制备低碳锰铁。通过热力学计算表明高碳锰铁焙烧氧化过程满足脱碳热力学条件,脱碳反应将进行。脱碳同时锰和铁也被氧化,在873 K分别氧化为Mn_2O_3和Fe_2O_3。温度高于1550 K时碳化锰将与氧化锰反应,真空下反应平衡温度降低,且体系压力越小,平衡温度就越低,当体系压力为2 Pa时,温度高于1030 K就可以进行脱碳。本文在热力学计算基础上开展高碳锰铁预氧化-真空脱碳实验研究,在焙烧氧化实验中,证实了脱碳反应的存在,焙烧3 h有13.17%碳被脱除。在真空脱碳实验阶段,延长保温时间及焙烧时间有利于碳的脱除,当高碳锰铁粉在873 K焙烧3 h,后在15 Pa下于1100℃脱碳4 h,成功制备出含碳0.47%的低碳锰铁。     

离子后氧化对42CrMo钢渗氮组织与耐蚀性的影响及机理分析

采用普通空气对42CrMo钢离子渗氮样进行了离子后氧化处理。采用金相、扫描电镜、X射线衍射仪、电化学性能分析测试仪对复合渗层的显微组织、渗层厚度、物相、耐蚀性及电化学试验后试样表面进行了测试和分析。研究结果表明,对42CrMo钢离子渗氮样进行空气后氧化处理可在氮化层表面形成一层1~2μm厚、由Fe3O4和Fe2O3组成的氧化层,且两种氧化物比值由后氧化工艺参数决定,400℃、60min后氧化时生成的氧化层Fe3O4含量最大,电化学实验后的试样表面没有出现点蚀现象,由此获得最佳耐蚀性。高含量Fe3O4基于该条件下生成Fe3O4的化学反应的吉布斯自由能较小。结果还发现随后氧化时间延长或温度升高,离子氮化层厚度逐渐减薄。     

表面纳米化预处理对316L不锈钢渗氮层摩擦学性能的影响

为改善奥氏体不锈钢的表面硬度和耐磨性,采用超声滚压与离子渗氮复合工艺对316L不锈钢表面进行了表面强化处理。利用扫描电镜(SEM)、硬度计、X射线衍射仪(XRD)和能谱仪以及摩擦磨损试验机等测定了渗氮层的硬度、深度、含氮量和物相组成,研究了表面晶层组织结构对离子渗氮行为和渗氮层在润滑油条件下摩擦学性能的影响。结果表明:直接渗氮和超声滚压/渗氮试样表层组织均由S、γ'、ε和Cr N相组成,渗氮层厚度均为20μm,直接渗氮层以S相为主,超声滚压后渗氮层以ε和γ'相为主,组织结构较为致密;超声滚压/渗氮层的平均渗氮含量是直接渗氮层的2.88倍,摩擦系数降低了0.04,显微硬度和耐磨性是直接渗氮层的1.15倍和2.76倍;超声滚压处理诱使316L不锈钢表面形成的纳米晶层组织结构增强了渗氮试样表面的催渗效能和对渗氮层的支撑强度,超声滚压后渗氮试样的表面耐磨性能最好。     

脱碳退火还原温度对高温Hi-B钢组织和磁性的影响

研究了脱碳退火后不同还原温度对高温Hi-B钢抑制剂、显微组织、织构、表面氧化层以及成品板磁性能的影响。结果表明,脱碳退火后提高还原温度减弱了表层抑制剂的作用,表层晶粒长大,促使表层的高斯组分进一步增强,使得轧向的(001)位向更为明显,有利于促进高温退火阶段高斯组分的二次再结晶,从而使最终产品形成强烈的高斯织构和完整的晶体组织。此外,提高还原温度,表面氧化膜中Fe含量下降,Si含量上升,使得氧化膜的结构更为致密,有利于发挥氧化膜在高温退火阶段的作用,从而使二次再结晶更完善,磁性能更优。     

稀土元素对中碳钢组织、力学性能和渗氮的影响

在一种中碳钢中通过添加微量稀土元素,研究稀土微合金化对钢的微观组织、力学性能以及在渗氮热处理条件下对渗层的影响.结果表明,添加稀土后,长条状的MnS夹杂和粗大块状的A12O3转变成小球状的稀土硫氧化物夹杂;铁素体的含量降低,并促进细小片层结构的珠光体形成;冲击性能提升126％以及塑性提高10％;渗氮处理后,添加稀土能显...     

Microstructure and Tribological Properties of Plasma Nitriding Cast CoCrMo Alloy

A medical cast CoCrMo alloy was coated by plasma nitriding process to enhance the wear resistance.The microstructures,phases and micro-hardness of nitrided layers were investigated by atomic force microscopy(AFM),scanning electron microscopy(SEM),X-ray diffraction(XRD) and micro-hardness.Tribological properties were investigated on a pin-on-disc wear tester under 25% bovine serum solutions.The experimental results showed that plasma nitriding was a promising process to produce thick,hard and wear resistant layers on the surface of CoCrMo alloy.The harder CrN and Cr2N phases formed on the plasma nitrided layer with the compact nano-crystalline structure.Compared with the untreated sample,all nitrided samples showed the lower wear rates and higher wear resistance at different applied loads and nitriding temperatures.It was concluded that the improvement of wear resistance could be ascribed to the formation of thicker and harder nitrided layers with the specific microstructures on nitrided surfaces.     

Influence of Ultrafine‐Grained Layer on Gaseous Nitriding of Large‐Sized Titanium Plate

In this paper, mechanical shot blasting on a large sized titanium plate is conducted to induce severe plastic deformation, which generates an ultrafine‐grained surface layer. The effect of an ultrafine‐grained layer on nitriding is evaluated at nitriding temperatures from 600 to 850 °C. The structural phases and mechanical property improvements are investigated and compared to those of a coarse‐grained specimen by using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and mechanical property measurements. The results indicate that an ultrafine‐grained layer enhances the nitriding kinetics and produces a thicker nitrided layer than that of a coarse‐grained plate at the same gaseous nitriding temperatures. The improved kinetics are attributed to a greater number of grain boundaries and defects introduced into the titanium plate surface by the mechanical shot blasting treatment. Meanwhile, the surface and cross‐sectional hardness values improve compared to the coarse‐grained plate due to the thicker nitrided layer resulting from deeper nitrogen diffusion.     

Effect of carbon addition on low-temperature plasma nitriding characteristics of austenitic stainless steel

Attempts have been made in the present work to investigate the influence of carbon in the treatment atmosphere on the low-temperature plasma nitriding characteristics of austenitic stainless steels. It was found that treatment gas composition has a significant effect on the structural characteristics of the nitrided layer. The addition of a small amount of carbon-containing gas such as methane (CH₄) to the treatment atmosphere can alter the structural development in the alloyed zone and offer several beneficial effects to the nitriding process. Based on this discovery, a new process has been developed, which involves the simultaneous incorporation of both nitrogen and carbon into the alloyed zone to form a dual-layer structure, which is free from chromium nitride, and carbide precipitates. Such a hybrid structure not only possesses larger layer thickness, high hardness, and more favourable hardness gradient than nitrided-alone layers, but also exhibits much improved corrosion resistance.     

H13钢气体氮化工艺参数的优化

运用正交试验法,研究H13钢气体渗氮工艺.以获得较高表面硬度和渗层厚度为依据,分析影响渗氮层结构和性能的主要工艺因素,确定出最佳工艺参数.采用光学显微镜及X射线衍射研究渗氮层的组织结构,采用显微硬度计测定化合物层的显微硬度.结果表明,影响渗氮层硬度和厚度的主要因素是渗氮温度和氛气分解率,最大渗层厚度为244.3μm,最...     

模具表面离子氮化工艺研究

研究了一种利用空气／甲烷混合气体对模具表面进行离子氮化的新工艺,分析了渗层的硬度、组织及物相。结果表明,通过加入甲烷气体,可以实现用空气直接进行离子氮化处理,通过调整甲烷流量,可以获得不同的渗氮硬度和物相。     

W18Cr4V高速钢离子渗氮层相结构与脆性研究

采用X射线衍射仪,金相显微镜及透射电镜分析W18Cr4V高速钢离子渗氮层相结构,采用连续加载压入法测定渗氮层脆性,分析了渗氮工艺对渗层相结构与脆性的影响。结果表明:离子渗氮工艺影响渗层相结构、含量及其分布,从而影响渗层脆性。     

Gaseous Nitriding Process of Surface Nanocrystallized （SNCed） Steel

The behavior of gaseous nitriding on the surface nanocrystallized(SNCed) steel was investigated.The mild steel discs were SNC ed on one side by using the method of ultrasonic shot peening.The opposite side of the discs maintained the original coarse-grained condition.The gaseous nitriding was subsequently carried out at three different temperatures;460,500 and 560℃ .The compound layer growth and diffusion behavior were then studied.It was revealed that SNC pretreatment greatly enhances both diffusion coefficient D and surface reaction rate.As a result ,nitriding time could be reduced to the half.It was also found that the growth of compound layer with nitriding time conformed with parabolic relationship from the start of nitriding process in the SNCed samples.     

Morphology Change in the Optical Microscopic Microstructure of Titanium by Nitriding Reaction and Combustion Synthesis Under Normal and Microgravity

Experiments on heating titanium wire specimens 0.5 mm in diameter by electric current in 0.5 absolute atmospheric pressure (0.5 kg/cm²) of a pure nitrogen gas environment under normal gravity (g = 9.8 m/s² = 1 G) and microgravity (g = G) using a drop shaft that enables 10 s of a microgravitational condition were carried out to investigate fundamentally the influence of microgravity on the reaction between Ti and nitrogen gas. The influence of gravitational acceleration on the morphological changes in optical microscopic microstructures of the specimens was studied. Under normal gravity, the thickness of the TiN layer resulting from the reaction of Ti and nitrogen gas at the outermost surface of the specimen increased with the heating time, but the tendency for the increase was reduced. A Widmanstätten structure, which is made by rapid heating and cooling of the specimen, was observed. However, the typical characteristics of the Widmanstätten structure vanished as the heating time proceeded. The progress of the nitriding reaction of the specimen was reduced, because heating by the electrical current and cooling by the convection of nitrogen gas balance each other out, and the temperature of the specimen became constant. Under microgravity, on the other hand, the thickness of the TiN layer of the outermost surface of the specimen increased with the heating time and was always thicker than that under normal gravity. The influence of microgravity, which suppresses the cooling effect of the thermal convection of nitrogen gas, on the nitriding reaction between titanium and nitrogen gas was significant. A dendritic structure caused by electrical heating was observed. Since the combustion synthesis of TiN was initiated at an elevated temperature after a certain heating time, huge dendritic structures were observed. The TiN tube was made on a final stage by leaching the titanium from the specimen. The influence of microgravity on the microstructure of the specimens that underwent nitriding was notable. Various results of the present study are explained by gravitational acceleration effects. The nitriding reaction became active by a temperature increase in the specimens with heating time due to the suppression of thermal convection and the cooling effect of the nitrogen gas on the specimens was reduced.