Properties and microstructure of Ti6Al4V by deformation accelerated low temperature plasma nitriding

An integrated low-temperature nitriding process was carried out for Ti6Al4V to investigateitseffect on microstructure and properties.The process was designed to enhance the nitriding kinetics in low-temperature（500℃） nitriding by deformation, and to strengthen Ti6Al4V alloybydispersionat the same time. Specimens of Ti6Al4V alloyweretreated through the process of solid solutionstrengthening-cold deformation-nitriding at 500℃. The white nitriding layeris formed after some time and then kept stable, changing little withthedeformationdegreeand time. The effect of aging on substrate is significant. Surface hardness and substrate hardnessincrease with deformation increasing. The construction was investigated by XRD.The surface nitridesare TiN, Ti2N, Ti4N3-Xand Ti3N1.29,and thenitridesin cross-section are Ti3N1.29and TiN0.3. The wear tests of specimens after nitriding, aging and deformation were carried out,andthetest data show that the nitrided pieces have the best wear resistance.

Microstructure of Surface Layer Formed at Low Temperature and High Carbon Concentration Carburizing with Rare Earth Element

A suitable carburized microstructure with fine granular dispersed carbides in hypereutectoid zone,ultra fine martensite in matrix and recrystallized austenite to be refined to the grain size of 12～14 has been obtained by a new process,which is a high carbon concentration carburizing with rare earth element at low temperature(860～880℃)in a discontinuous gas carburization furnace.There was not much difference for the microstructure in eutectic zone between this and conventional process.Forming mechanism of granular carbides has been also studied in this paper.

IMPROVEMENT OF MECHANICAL PROPERTIES OF MARTENSITIC STAINLESS STEEL BY PLASMA NITRIDING AT LOW TEMPERATURE

A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.

Effect of Rare Earth Elements on Powder Boro-Carbo-Nitriding at Low Temperature

The process of the co-cementation layers of low temperature powder multicomponent thermochemical treatment with B-C-N-RE and the structure and properties were studied and compared with those of conventional boro-carbo-nitriding (B-C-N) by X-ray diffractometer, potentiostat and wear machine. The results show that rare earth elements have significant catalytic effect within proper limits. Both wear resistance and corrosion resistance of the B-C-N-RE co-cementation layer are greatly increased in comparison with those of the B-C-N. The function mechanism of rare earth elements is also discussed.

Investigations on the Corrosion Behaviour and Structural Characteristics of Low Temperature Nitrided and Carburised Austenitic Stainless Steel

The wear resistance of austenitic stainless steels can be improved by thermo-chemical surface treatment with nitrogen and carbon. However, it is possible that the corrosion resistance will be impaired by the precipitation of chromiumnitrid or -carbide. The present contribution deals with investigations of the corrosion behaviour and structural characteristics of a low temperature nitrided and carburised austenitic stainless steel. The material investigated was AISI 316L (X2CrNiMol7-12-2) austenitic stainless steel. A commercial plasma-nitriding unit (pulsed dc) was used for the nitriding and carburising process. Additional samples were treated by the gasoxinitriding process for a comparison between plasma- and gasoxinitriding. The nitrided and carburised layer of austenitic stainless steel consists of the nitrogen or carbon S-phase (expanded austenite), respectively. X-ray diffraction investigations show the typical shift of the peaks to lower angles, indicating expansion of the fee lattice. Also the X-ray diffraction technique was employed to study the residual stresses in the nitrogen and carbon S-phase. The corrosion behaviour of surface engineered samples was investigated with electrochemical methods. Anodic potentiodynamic polarisation curves were recorded for testing the resistance against general corrosion (in H2SO4) and pitting corrosion (in NaCl).

Study on Carburizing Kinetics of Low-carbon Steel at High-temperature and Short-term

In this paper, the carburizing kinetics of low-carbon steel at high-temperature and short-term in liquid cast-iron were studied by metallographic microscope, chemical analysis and so on, and the microstructure of carburized layer was also analyzed. The results show that the carburizing rate of low-carbon steel at high-temperature and short-term is so fast, and the microstructure of carburized layer possess higher carbon content, and cementite, pearlite and ferrite exist in carburized layer structure simultaneously. Besides, the kinetic equations of permeating layer forming have been presented, and the carburizing mechanism was preliminary discussed also.

Layer Structure Analysis of Low-Carbon Steel Containing Rare Earth by High-Temperature Carburizing of Liquid Cast-Iron

The layer structure of low-carbon steel containing RE by high-temperature (T>1200 ℃) carburizing of liquid cast-iron was studied and the diffusion activation energy of carbon was calculated by metallographic microscpe, chemical analysis etc. The result shows that the technology of carburizing in liquid cast-iron can expedite caburization distinctly and changes the carburizing layer structure. The carburizing rate is 60～80 times of that of the traditional technology, and there is about 43% decrease in the activation energy compared with gas-carburization. In outer structure layer, cementite is formed simultaneously both on the crystal boundary reticularly and inside the crystal grains stripedly. In inner carburizing layer, there is undissolved blocky ferrite in reticular cementite. Besides, rare earth element can expedite carburization process.

Microstructure and Properties of Low Temperature Composite Chromized Layer on H13 Tool Steel

Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography, X-ray diffraction, microanalysis, hardness and wear tests. It was found that this low temperature process was thermo-dynamically and kinetically possible, and the composite chromized layer on H13 steel, with a thickness of 3-6 μm, consisted of three sub-layers (bands), viz. the outer Cr-rich one, the intermediate (black) one, and the inner, original white layer. After chromizing, the former diffusion layer was thickened. The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN, Cr2N, (Cr, Fe)23C6, and (Cr, Fe)7C3, as well as plain α-(Fe, Cr). A high surface microhardness of 1450-1550 HV0.025, which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding, was obtained. In addition, an excellent wear resistance was gained on the composite chromized layer.

Wear resistance of TC4 by deformation accelerated plasma nitriding at 400 °C

An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400℃, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti3N（2-X）. The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.

Low-Cost Preparation of Boron Nitride Ceramic Powders

The amorphous boron nitride ceramic powders were prepared at 750-950 ℃ by the low-cost urea route, and the effects of preparation temperatures, molar ratios of the raw materials and oxidation treatment on the composition, structure and surface morphology of the products were investigated through FT-IR, XRD and SEM. The results show that the products ceramize and crystallize gradually with the increase of the temperature. When the molar ratio and reaction temperature are 3：2 and 850 ℃, respectively, the products have high purity, compact structure and nice shape. The oxidation treatment at 450 ℃ will not impair the composition and structure of boron nitride but effectively remove the impurities.

Low temperature sintering and performance of aluminum nitride/borosilicate glass

Aluminum nitride （AlN）/borosilicate glass composites were prepared by the tape casting process and hot-press sintered at 950 ℃ with AIN and SiO2-B203-ZnO-Al2O3-Li2O glass as starting materials. We characterized and analyzed the variation of the microstructure, bulk density, porosity, dielectric constant, thermal conductivity and thermal expansion coefficient （TEC） of the ceramic samples as a function of AIN content. Results show that AIN and SiO2-B2O3-ZnO-Al2O3-Li2O glass can be sintered at 950 ℃, and ZnAI204 and Zn2SiO4 phase precipitated to form glass-ceramic. The performance of the ceramic samples was determined by the composition and bulk density of the composites. Lower AlN content was found redounding to liquid phase sintering, and higher bulk density of composites can be accordingly obtained. With the increase of porosity, corresponding decreases were located in the dielectric constant, thermal conductivity and TEC of the ceramic samples. When the mass fraction of AlN was 40%, the ceramic samples possessed a low dielectric constant （4.5-5.0）, high thermal conductivity （11.6 W/（m.K）） and a proper TEC （3.0× 10^-6 K^-1 which matched that of silicon）. The excellent performance makes this kind of low temperature co-fired ceramic a promising candidate for application in the micro-electronics packaging industry.

低温液体氧氮化对奥氏体不锈钢磨损行为的影响

[目的]奥氏体不锈钢被广泛用于制造各种航空电子装备零部件,但其硬度和耐磨性欠佳。[方法]采用低温液体氧氮化技术对304奥氏体不锈钢进行表面改性处理。采用扫描电子显微镜、透射电子显微镜、维氏硬度计等分析了所得复合改性层的微观组织和截面显微硬度分布,通过摩擦磨损试验探究了表面改性层的耐磨性。[结果]低温液体氧氮化表面改性层由外侧致密的Fe_(3)O_(4)相和内侧富氮S相构成。S相是含氮过饱和固溶体,含有大量位错、层错和孪晶,因此硬度较高。载荷和温度会影响不锈钢样品的磨损行为,温度升高和载荷增大都会使304奥氏体不锈钢样品和低温液体氧氮化样品的平均摩擦因数轻微下降,磨损体积损失增大。不过低温液体氧氮化处理能够缩短304奥氏体不锈钢样品初始磨损阶段的持续时间,使其在载荷10 N、温度200℃条件下的最大磨损体积损失由1.086 mm^(3)降至0.144 mm^(3)。[结论]低温液体氧氮化处理能够显著提高304奥氏体不锈钢的耐磨性。

奥氏体不锈钢渗碳层的组织及耐蚀强化性能研究

针对常规渗碳工艺会削弱奥氏体不锈钢耐蚀性的问题,通过对现有气体渗碳技术进行改进,采用前处理活化、降低渗碳温度的方法,实现了奥氏体不锈钢渗碳兼顾表面强度与耐蚀性能的目标。采用该工艺对AISI304和AISI316奥氏体不锈钢进行渗碳处理,并分析渗层组织和性能,结果表明,在470℃条件下,AISI316不锈钢经气体渗碳处理后,渗碳层具有优异的耐蚀强化性能。

0Cr18Ni9不锈钢表面纳米化组织及其热稳定性对低温渗氮行为的影响

采用超音速微粒轰击技术(SFPB)对0Cr18Ni9不锈钢试样进行了表面纳米化处理,并对SFPB处理后的试样进行热处理和低温气体渗氮处理,分析讨论了表面纳米化组织及其热稳定性对低温渗氮行为的影响.结果表明:经SFPB处理后,试样表层形成厚约250μm的变形区,表面组织为纳米晶,平均晶粒尺寸为15 nm,其变形机制以孪生为主,变形同时表面发生了马氏体相变,表面硬度明显提高.对SFPB处理的试样经450℃热处理后,纳米晶未发生明显粗化,马氏体量减少很小,硬度保持稳定,因而具有良好的热稳定性.晶粒细化、马氏体相变及其良好的热稳定性有利于实现低温快速渗氮,使渗层厚度明显增加,表层硬度得到进一步提高,硬度分布梯度也得到了改善.

奥氏体不锈钢低温气体渗碳的组织性能

低温盐浴渗碳、等离子渗碳等低温渗碳工艺在提高奥氏体不锈钢表面强度的同时,会降低其耐蚀性能。为克服上述缺陷,开发了一种高效兼顾表面强度与耐蚀性能的表面强化工艺的低温气体渗碳技术。采用该工艺对304、316奥氏体不锈钢进行渗碳处理,并对得到的奥氏体不锈钢低温渗碳组织性能进行分析。结果表明,随着温度升高,试样表面强度提高,而腐蚀性能下降。470℃是兼顾强化与耐蚀性能的低温气体渗碳工艺参数。

流延法制备低温烧结的高热导率AlN基片

本文研究了流延法制备低温烧结的高热导率ＡｌＮ基片过程中影响流延浆料粘度的主要因素，结果表明，溶剂比例的增加会导致浆料粘度下降，增塑剂的减少则使粘度上升．本文还研究了添加剂对ＡｌＮ陶瓷烧结及热导性能的影响，实验表明Ｂ２Ｏ３能以过渡液相的形式促进烧结，而Ｄｙ２Ｏ３在低温下具有较好的去除ＡｌＮ晶格氧的能力．通过添加Ｄｙ２Ｏ３、Ｂ２Ｏ３等组成的混合助烧结剂；在１６５０℃下烧结４ｈ，获得了热导率高达１３０Ｗ／ｍ·Ｋ的ＡｌＮ基片．

离子轰击热处理技术对轴承钢摩擦学性能的影响

为提高轴承钢的摩擦磨损性能,采用离子轰击热处理技术在GCr15轴承钢的表面生成渗硫层、渗氮层和硫氮复合渗层。在球—盘摩擦磨损试验机上对比研究轴承钢原始表面、渗硫表面,渗氮表面与硫氮复合处理表面在油润滑下的摩擦磨损性能。利用显微硬度计分析不同表面的硬度;利用扫描电镜观察不同处理表面和磨损表面的形貌;利用X射线光电子能谱仪分析磨损表面边界润滑膜化合物的价态并研究元素随深度的变化。研究表明,GCr15轴承钢表面通过渗硫、渗氮、硫氮复合处理后在油润滑条件下摩擦磨损性能都可以得到比较明显的提高。轴承钢基体对渗硫层的支持作用有限,影响硫化层作用的发挥。高硬度的渗氮层在较低载荷下可以起到很好的减摩抗磨作用。硫氮复合处理盘由于在较软的共渗层下面存在高硬度的渗氮层,可以对表面的软质层提供更强的支持,在较苛刻的工况下,硫氮复合盘的摩擦学性能显得更加突出。

低温离子渗氮提高2Cr13不锈钢的冲蚀磨损与冲刷腐蚀抗力

采用喷射式固体粒子冲蚀磨损实验机和浆体冲刷腐蚀装置对比研究了350℃低温离子渗氮和550℃常规高温离子渗氮对2Cr13不锈钢冲蚀磨损和冲刷腐蚀行为的影响规律,通过组织结构分析、硬度测试和电化学交流阻抗分析探讨了低温渗氮改善2Cr13不锈钢抗冲蚀磨损和抗冲刷腐蚀性能的机制。结果表明:低温和常规高温离子渗氮均可提高2Cr13不锈钢在小角度固体颗粒干冲蚀条件下的冲蚀磨损抗力,但是,350℃低温渗氮处理表现出比550℃高温离子渗氮层更好的抗冲蚀磨损性能。在含10%石英砂的中性和酸性5%NaCl水溶液中,350℃低温渗氮处理使2Cr13不锈钢冲刷腐蚀速率分别降低96.7%和87.4%;然而,550℃常规离子渗氮却导致2Cr13不锈钢冲刷腐蚀速率分别提高4.13倍和0.49倍。350℃渗氮层由-εFe3N和N过饱和固溶体αN相组成,其化学稳定性好,硬度高,因而表现出良好的耐腐蚀、抗冲刷磨损与抗冲刷腐蚀性能。550℃渗氮处理时,αN相分解成了α相和CrN化合物,造成基材贫Cr,耐腐蚀性能下降,同时表面硬度低于350℃低温渗氮层,其抗冲蚀磨损性能不及350℃低温渗氮处理,冲刷腐蚀抗力则低于2Cr13不锈钢基材。

低温共烧多层AlN陶瓷基片

介绍了由高热导率AlN陶瓷与金属W制备的低温共烧多层AlN基片研究了以Dy2O3为主的添加系统对低温烧结AlN性能、显微结构的影响以及制备低温共烧基片的关键工艺，如排胶、烧成等，结果表明：以Dy2O3为主的添加系统可有效地降低烧结温度和去除AlN晶格氧在1650℃的氮中无压烧结4h，热导率达130W（m·K）-1;两步排胶法可以较好地解决W氧化及AlN晶粒表面吸附残余碳的问题；烧结时在1400～1650℃慢速升温。

12Cr2Ni4A钢高温真空低压脉冲渗碳工艺

与传统气氛渗碳相比,高温真空渗碳在提高渗碳效率、产品质量和节约能源方面均表现出明显优势.本文分析了12Cr2Ni4A钢的奥氏体晶粒长大行为、扩散系数及奥氏体饱和碳质量分数等关键参数的影响,结合真空低压脉冲渗碳工艺原理,对高温真空低压脉冲渗碳工艺进行实验验证.结果表明:实验钢在930,950,980℃渗碳温度下,渗碳层的硬度梯度曲线和碳质量分数梯度曲线的实测值与预期值吻合较好.此外,随着渗碳温度的升高,碳的扩散系数和奥氏体饱和碳质量分数增加,高温真空渗碳可显著提高渗碳速率,温度每提高10℃约使渗碳效率提高14%~17%.