NiCrAlY涂层的表面状态对高温氧化行为的影响

将原始喷涂态和表面抛光的NiCrAlY涂层在1050℃恒温氧化300h，利用XRD、SEM，EDS方法，测定涂层的氧化物及其相转变，分析表面氧化膜的生长破坏行为，结果表明：两种涂层在1050℃保温，在150h以内均能生成α-Al2O3氧化膜，150h后，抛光态涂层保护性氧化膜被破坏，抗氧化能力下降，喷涂态涂层表面粗糙，连续Al2O3保护膜的形成较晚，氧化早期氧化膜中存在微裂纹，可释放应力，有利于氧化膜与涂层的结合。氧化动力学曲线符合抛物线规律，氧化至300h，表面氧化膜只有少量微裂纹，无剥落，说明喷涂涂层的长期恒温抗氧化能力比抛光态涂层强。     

Prediction of surface and interfacial tension based on thermodynamic data and CALPHAD approach

In this article, following a brief introduction concerning experimental measurements of surface and interfacial tensions, methods for calculating surface tension and surface segregation for binary, ternary, and multicomponent high-temperature melts based on Bulter＇s original treatment [ 1] and on available physical properties and thermodynamic data, especially excess Gibbs free energies of bulk phase and surface phase versus temperature obtained from thermodynamic databases using the calculation of phase diagram （CALPHAD） approach, with special attention to the model parameter β, have been described. In addition, the geometric models can be extended to predict surface tensions of multicom- ponent systems from those of sub-binary systems. For illustration, some calculated examples, including Pb-free soldering systems and phase-diagram evaluation of binary alloys in nanoparticle systems are given. On the basis of surface tensions of high-temperature melts, interracial tensions between liquid alloy and molten slag as well as molten slag and molten matter can be calculated using the Girifalco-Good equation [2]. Modifications are suggested in the Nishizawa＇s model [3] for estimation of interracial tension in liquid metal （A）/ceramics （MX） systems so that the calculations can be carried out based on the sublattice model and thermodynamic data, without deliberately differentiating the phase of MX at high temperature. Finally, the derivation of an approximate expression for predicting interfacial tension between the high-temperature multicomponent melts, employing Becker＇s model [4] in conjunction with Bulter＇s equation and inteffacial tension data of the simple systems is described, and some examples concerning pyrometallurgical systems are given for better understanding.     

A new method of fast measuring surface tension of melt cast iron and its application in graphite shape identification

1. Introduction In a casting process of alloy, many casting process parameters, such as refining and inoculating, gas isolation, mould filling ability and the surface roughness of casting, relate to surface tension of alloy. So, it has been approa- ched for a long time of interest by foundrymen and metallurgists to invent an effective method of fast measuring surface tension. Traditional methods of measuring surface tension can be classified into static and dynamic methods. Static method calcu…     

Nanoindentation on the surface of thermally sprayed coatings

The ability to quantify surface mechanical properties is valuable for assessing the quality of thermal spray coatings. This is especially important for prostheses where loading is placed directly on the surface. Hydroxyapatite was classified to small (20-40 μm), medium (40-60 μm) and large (60-80 μm) particle sizes and thermal sprayed to produce a coating from spread solidified hydroxyapatite droplets. It was revealed for the first time, that nanoindentation can be successfully used to determine the hardness and elastic modulus on the surface of well spread solidified droplets at the hydroxyapatite coating surface. Comparison with indentation results from polished cross-section exhibited comparable values and statistical variations. The hardness was 5.8 ± 0.6, 5.4 ± 0.5 and 5.0 ± 0.6 GPa on coatings produced from small, medium and large sized powder. Similarly, the elastic modulus decreased from 121 ± 7, 118 ± 7 to 114 ± 7 GPa, respectively. Use of several indentation loads gave comparable results with sintered hydroxyapatite suggesting good inter-splat bonding within the coating. MicroRaman spectroscopy and X-ray diffraction confirmed a larger degree of dehydroxylation for the smaller particles also revealing a lower elastic modulus. This shows the influence of particle size and possibly dehydroxylation of hydroxyapatite on the mechanical properties of the coating surface.     

由铁液表面张力预测和防止灰铸铁针孔缺陷

介绍了灰铸铁件针孔缺陷形成的原因及其与铁液表面张力的关系：认为表面张力越大,针孔缺陷越难形成;阐述了表面张力的测量方法,并提出了表面张力防止针孔的措施。     

Influence of surface roughness on performance of zinc-rich paint coatings

The influence of surface roughness on the performance of zinc-rich paint(ZRP) coatings was studied.Electrochemical impedance spectroscopy(EIS) measurements were used to assess the corrison prevention performance of the ZRP coatings.Furthermore,the EIS data of the steel-ZRP-sea water system were interpreted according to equivalent circuit models and the corresponding parameters were derived to assess the coating deterioration with time.The results show that the rougher surface favors better protection effect of the ZRP coatings.The protection potential of ZRP coatings for the standards and codes of practice is -0.78V(vs SCE).     

离子轰击下高碳钢的脱碳对随后渗金属的影响

研究了T8钢等离子体脱碳对随后渗金属的影响. 介绍了两种处理工艺, 一种是脱碳后渗金属, 另一种是直接渗金属. 结果表明, 在离子轰击下, 高碳钢表层产生严重的脱碳层, 脱碳层的存在对随后的渗金属过程有着很大的影响. 脱碳后渗金属, 渗层厚度达80μm; 直接渗金属, 渗层厚度仅15μm. 在两种渗金属条件下, 表面合金层的非碳化物形成元素Co含量差别不是很大, 而强碳化物形成元素W和Mo的含量却有着显著差异, 直接渗金属的, 表层W和Mo含量几乎为零, 而脱碳后渗金属的, 表层W和Mo总量最大达到6%左右.     

Effect of steam treatment during plasma spraying on the microstructure of hydroxyapatite splats and coatings

The major problems with plasma sprayed hydroxyapatite (HA) coatings for hard tissue replacement are severe HA decomposition and insufficient mechanical properties of the coatings. Loss of crystalline HA after the high-temperature spraying is due mainly to the loss of OH⁻ in terms of water. The current study used steam to treat HA droplets and coatings during both in-flight and flattening stages during plasma spraying. The microstructure of the HA coatings and splats was characterized using scanning electron microscope, Raman spectroscopy, Fourier transform IR spectroscopy, and x-ray diffraction. Results showed that a significant increase in crystallinity of the HA coating was achieved through the steam treatment (e.g., from 58 to 79%). In addition, the effects were dependent on particle sizes of the HA feedstock, more increase in crystallinity of the coatings made from smaller powders was revealed. The Raman spectroscopy analyses on the individual splats and coatings indicate that the mechanism involves entrapping of water molecules by the individual HA droplets upon their impingement. It further suggests that the HA decomposition has already taken place before the impingement of the droplets on precoating or substrate. The improvement in crystallinity and phases, for example, from tricalcium phosphate and amorphous calcium phosphate to HA, was achieved by reversing the HA decomposition through providing extra OH⁻. Furthermore, the steam treatment during the spraying also accounts for remarkably increased adhesion strength from 9.09 to 23.13 MPa. The in vitro testing through immersing the HA coatings in simulated body fluid gives further evidence that the economic and simple steam treatment is promising in improving HA coating structure. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

5052铝合金表面化学镀Ni-P镀层的组织与性能

利用化学镀在5052铝合金表面制备了Ni-P镀层,通过SEM、EDS和XRD等手段对镀层表面和界面的形貌、物相、组成、结构和性能进行了表征和分析。结果表明:化学镀Ni-P合金镀层为非晶态,成分以Ni为主,由直径为10~50-m的颗粒组成,颗粒分布较均匀,界面结合状态良好;化学镀对表面粗糙度的影响在500 nm以内,镀后镀层表面粗糙度Ra为384.49 nm;镀层残余应力状态为拉应力,其值达到(521±168.0)MPa。     

Effect of Nd and La on surface tension and wettability of Sn-8Zn-3Bi solders

Maximum bubble pressure measurement was employed to evaluate surface tension of Sn-8Zn-3Bi- （0-0.15）Nd and Sn-8Zn-3Bi-（0 -0. 15）La solder melts. Wetting balance method was used to measure wetting force and wetting time on Cu substrate of the two group solders. The experimental results show that minute amount of Nd or La addition to Sn-8Zn-3Bi solder causes significant decrease of the surface tension of the solder melts at 200 - 240 ℃ and Nd addition is more effective on reduction of surface tension than that of La. Nd or La addition has the effect on enhancing the wetting force of the solder melts on Cu substrate, which results from the de- crease of interracial tension between the solder melt and Cu substrate. The wetting force reaches the maximum when 0.1% Nd is added to the base alloy. The contact angle between Sn-8Zn-3Bi base solders and Cu substrate decreases with the addition of Nd or La and the minimum of the contact angle is obtained from the solder with 0.1% Nd addition.     

成形磨削表面粗糙度的试验研究

数控成形磨削技术是近年来国内外迅速发展的一种新型的加工技术,其高效精密的加工方式在机械工程上有着极其广泛的应用。本文首先分析了成形磨削过程中各磨削参数对磨削表面粗糙度的影响,进而对金刚石滚轮修整轨迹进行推导和分析,验证了修整条件和磨削条件对成形磨削表面粗糙度的影响。本文运用正交回归设计方法建立了表面粗糙度R。对磨削工艺参数的回归方程,并推导出模型公式Ra=2．34×V(?)/-0.45×Vω/0.08×aρ/0.15,找出磨削工艺参数对Ra的影响程度,在实际应用中可以对Ra进行预测。在研究修整轨迹在某点的曲率半径ρ与修整速比q的变化关系时,测定了不同的修整速比p,每转进给量与表面粗糙度的变化关系。研究结论可用于分析和预测fd或限制工件表面粗糙度。     

Tribological properties of titanium aluminides coatings produced on pure Ti by laser surface alloying

Titanium aluminides coatings were in-situ synthesized on a pure Ti substrate with a preplaced Al powder layer by laser surface alloying. The friction and wear properties of the titanium aluminides coatings at different normal loads and sliding speeds were investigated. It was found that the hardness of the titanium aluminides coatings was in the following order: Ti₃Al coating > TiAl coating > TiAl₃ coating. Friction and wear tests revealed that, at a given sliding speed of 0.10 m/s, the wear volume of pure Ti and the titanium aluminum coatings all increased with increasing normal load. At a given normal load of 2 N, for pure Ti, its wear volume increased with increasing sliding speed; for the titanium aluminides coatings, the wear volume of Ti₃Al coating and TiAl coating first increased and then decreased, while the wear volume of TiAl₃ coating first decreased and then increased with increasing sliding speed. In addition, the friction coefficients of pure Ti and the titanium aluminides coating decreased drastically with increasing sliding speed. Under the same dry sliding test conditions, the wear resistance of the titanium aluminium coatings was in the following order: Ti₃Al coating > TiAl coating > TiAl₃ coating.     

Effect of substrate surface roughness on the adherence of NiCrAlY thermal spray coatings

The adherence of plasma sprayed NiCrAlY bond coats can be improved by an appropriate substrate surface finish. The interface fracture energy for crack propagation along the coating/substrate interface has been measured for different surface roughness by means of a specially designed four-point bending test. An increase of the interface fracture energy of about 15% was observed for a three times higher surface roughness. In addition, four-point bending tests with the coating on the side face of bending specimens were performed to analyze the fracture and spalling behavior of the coatings both under large tensile and compressive substrate deformations.     

铝板带虎皮纹浅析

确认了铝板带虎皮纹是在连铸连轧过程中产生的,并对其特点进行了研究,从理论上解释了虎皮纹产生的机理,提出了消除此缺陷的方法。     

冷轧钢渗碳处理后的ELID磨削效果及加工表面硬度实验研究

本文采用在线电解修整磨削技术,对经渗碳处理后的冷轧钢进行超精密镜面磨削试验,获得表面粗糙度达Ra6～8 nm的加工表面.实验结果表明:采用微细粒度、高硬度铸铁基金刚石砂轮、提高砂轮线速度和减小磨削深度可有效地提高表面质量,降低表面粗糙度;磨削过程中,砂轮线速度、磨削深度、磨削液是影响加工表面质量的主要因素.     

扫描速度对共析钢等离子表面淬火硬化的影响

以层流等离子弧作为热源对共析钢进行表面淬火,通过等离子表面淬火热传导的理论分析,对等离子弧扫描速度对硬化层最大硬化深度的影响进行研究。并利用电子扫描显微镜、显微硬度计等试验手段,研究了淬火硬化层的显微组织和力学性能。结果表明:层流等离子弧扫描速度越快,淬火硬化层最大硬化深度越小。得出等离子弧扫描速度与淬火硬化层最大硬化深度之间的关系,并且与实验结果相吻合。淬火硬化层组织为板条状马氏体和针状马氏体,淬火硬化层与基体的界面组织为珠光体和隐针马氏体,基体组织为珠光体。淬火硬化层硬度由共析钢基体的350 HV提高到900～1000 HV。     

使用半工业化机械浮选机评估矿浆黏度变化对浮选气泡大小的影响

浮选过程中矿浆的黏稠度是由矿浆温度、矿粒浓度、矿粒细度等决定,它对浮选效率的影响一直受到工业界的极大重视。在实际生产中,一些自然因素和操作参数的变化,如季节性温度的浮动,矿石硬度、矿石性质的变化等产生的矿浆黏稠度的浮动,导致气泡尺寸和分布规律产生浮动,进而使选矿回收率等经济指标下滑。即便如此,在科研中矿浆黏稠度的相关研究并未受到重视。本研究的重点是黏稠度和气泡尺寸在浮选过程中的关系。试验采用半工业化美卓700 L机械浮选机和McGill大学独有的气泡观测仓,通过调整液体温度来改变黏稠度,在充分屏蔽其他浮选操作条件的情况下形成了气泡-黏稠度的关系图。结果显示了气泡尺寸D32和黏稠度（μ/μ20）之间呈现0.776的指数关系,有较强的关联性。本研究结果对实际生产中通过控制黏稠度来优化气泡尺寸,乃至浮选经济指标具有借鉴意义。     

Effects of alternative electromagnetic field on surface tension and filling ability of molten metal

Surface tension and filling ability of molten metal play an important role on the shaping of the molten metal. The surface tension was calculated from wetting angles of the molten metal by the sessile drop method. The specimen for filling ability was designed and the filling ability experiments under the alternative electromagnetic field were performed. The results show that the intensity and frequency of the alternative electromagnetic field have significant effects on the surface tension of the molten metal. The surface tension of Al-6% Si alloy decreases with increasing the intensity of the electromagnetic field. For pure Sn, the surface tension decreases gradually when the frequency of electromagnetic field is reduced. The filling ability is improved by applying the alternative electromagnetic field.     

A correlation between the hydrophilicity of a metal and its surface tension. Calculation of the bond energy of water molecules adsorbed on an uncharged metal surface

The surface tension of a metal is shown to be a qualitative characteristic of its hydrophilicity. A technique of the estimation of the bond energy of the water molecules adsorbed on a metal surface is proposed. The bond energies between the water molecules and smooth nonoxidized uncharged surfaces of various metals are calculated. The experimental data on the adsorption of surface active substances on an iron electrode are analyzed.