Surface characteristics and wear performance of laser surface engineered iron oxide coatings on cast aluminium alloy

Abstract

Surface characteristics of laser surface engineered iron oxide coatings on a cast aluminium alloy developed for improved wear performance have been studied by atomic force microscopy (AFM) in association with microhardness measurements. An attempt is made to relate the grain size and surface roughness of FeO and Fe₃O₄ based coatings to wear performance determined by block-on-disk dry sliding wear testing. Fe₃O₄ based coating exhibits finer grain and smoother surface in comparison to FeO coating. However, FeO displays superior wear performance even though the Knoop microhardness of both coatings was comparable.     

Thermography during laser surface melting of cast aluminium alloy

Abstract

In situ high speed IR thermographs captured during laser surface melting of A319 enabled estimation of maximum temperature, temperature gradient and cooling rate. In light of limited spatial and time resolutions of the IR camera, a one-dimensional heat transfer model was adopted for estimating the cooling rate. The cooling rate so estimated provided a range of cell size that closely matched with the experimentally observed cell size.     

不同表面处理对灰铸铁摩擦学性能的影响

分别对灰铸铁样件进行磷化处理、磷化+纳米铁基离子表面处理、磷化+二硫化钼粘结固体涂层处理,在浸油润滑条件下,采用万能摩擦试验机,考察灰铸铁在不同表面处理下的摩擦磨损性能。试验结果表明,磷化+二硫化钼粘结固体涂层试件的摩擦系数最低,稳定在0.125左右,并出现少量的粘着磨损和磨粒磨损。     

Structure and properties of resistive thick films after laser treatment

We have studied the influence of laser radiation on the structure and electrophysical properties of resistive thick films based on BaB₆-LaB₆ solid solution. It has been shown that, in the course of laser treatment in the millisecond range, barium and lanthanum diffuse into the substrate, and micro-and nanosecond laser radiation leads to the breakup of current-conducting chains and the formation of domains with discrete structure. We have carried out a differential analysis of voltampere characteristics and determined the temperature dependences of electrical resistance R and resistance temperature coefficient. Laser treatment in the micro-and nanosecond ranges slightly increases the electrical resistance, which can be used for the precision treatment of thick films. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 79–85, November–December, 2007.     

铸铁表面激光熔敷镍基合金涂层的耐磨性研究

为了提高铸铁的耐磨性,以35％WC和不含WC的镍基合金粉末为原料对铸铁表面进行激光熔敷处理,利用XRD、SEM、TEM等技术分析了涂层的成分及显微组织结构,并测试了涂层的耐磨性和硬度．结果表明：激光处理后表面迅速熔化和冷却,组织由珠光体 片状石墨组织转化为不同粗细的针状马氏体与残余奥氏体组织;熔敷层的耐磨性和硬度明显提高,且添加35％WC硬质颗粒的熔敷层硬度最高值不在最表层,而在距表面约0．2mm处;合金涂层在磨损机制下表现为犁沟切削、微切削以及硬相质点的剥落,不同基体划痕形式不同。     

Investigation on mechanical properties and tribological behaviour of stir cast LM13 aluminium alloy based particulate hybrid composites

LM13 aluminium alloy with boron carbide (0 wt.%–7.5 wt.%) and fly ash (2.5 wt.%) reinforced particulate hybrid composites were fabricated using liquid metallurgy route. Microstructure and mechanical properties viz., hardness, ultimate tensile strength and ductility were investigated. Wear behaviour of composites was tested by varying sliding distance and load. Fracture surface and worn surface of composites were examined using field emission scanning electron microscope. Microstructure of hybrid composites revealed uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt.% of boron carbide and fly ash particles. Wear test results showed that addition of particles significantly decreased the weight loss and coefficient of friction. Also cumulative weight loss decreased up to 47.2 % for 10 wt.% of hybrid composites as compared to LM13 aluminium alloy. Fracture surface of composites showed dimples with particle cracking on the surface. Worn surface of LM13 aluminium alloy showed continuous grooves due to ploughing with delamination. However, worn surface of composites showed fine grooves due to the presence of hard reinforcements on the surface. Boron carbide and fly ash reinforced LM13 aluminium hybrid composites exhibited superior mechanical properties with excellent wear resistance as compared to LM13 aluminium alloy.     

Structure and vibration characteristics of Ti-Al-Mo-V alloy

Ti-5Al-2.5Mo-1.4V rolled plates were subjected to solid-solution heat treatment at 870 or 930^∘C for 1 h and aged for 1–8 h at 460^∘C to investigate the relationship between the microstructure and the vibration characteristics of the alloy. According to the experimental results, the S870 solid solution matrix contains α + α′ + β structures and the S930 solid solution specimen possesses α +α′ structures (β transus is ∼ 900^∘C). Increasing the α′ phase content improves strength and hardness but reduces ductility. It also promotes internal friction and thus increases damping. During the 460^∘C aging process, the α′ phase in the β region of S870/Ah grows and transforms into a finer needle structure and the primary α phase (bounded by prior β grain boundary) of S930/Ah grows within the α′ matrix. Both S830/Ah and S930/Ah reveal similar tendencies in mechanical properties with increased aging time. When the aging time exceeds 1 h, S870/Ah, having a large quantity of β phase, has a better vibration damping ratio than S930/Ah (containing a great quantity of primary α phase).     

冷热循环处理对钛基非晶合金摩擦学性能的影响EI北大核心CSCD

钛合金的耐磨性较差,在钛合金活动部件表面制备钛基非晶合金涂层是一种保持钛合金优势又提升其耐磨性的选择。采用X射线衍射仪、差示扫描量热仪、SEM、摩擦磨损试验机,对冷热循环处理前后钛基块体非晶合金的组织结构与摩擦行为进行比较研究。结果表明:经过冷热循环处理后的钛基块体非晶合金仍然保持着完全非晶态,弛豫焓提升11%。冷热循环处理后钛基非晶合金的平均纳米硬度从6.84 GPa降低到6.59 GPa,平均弹性模量从118.70 GPa降低到103.43 GPa,但硬度与弹性模量的比值增大。冷热循环处理后,钛基块体非晶合金在5 N和10 N的载荷下磨损率减小了约10%。与TC4合金相比,其在5 N和10 N载荷下的磨损率分别减小了20%和50%。TC4合金由于硬度较低,呈现较为严重的黏着磨损。冷热循环处理后,钛基非晶合金的磨损机制从铸态的磨粒磨损为主向磨粒磨损、黏着磨损和氧化磨损共同作用转变,且随着载荷的增大,黏着磨损减轻,磨粒磨损占据主导。因此,冷热循环处理是提升钛基块体非晶合金摩擦学性能的一种有效方法。     

铸造Mg-RE合金的显微结构及其蠕变行为

研究了铸造Mg-RE合金的高温蠕变特性,通过SEM和TEM观察,讨论与分析了该合金的蠕变机制.结果表明:在473K、应力低于100MPa条件下,该合金具有良好的蠕变抗力,其稳态蠕变速率低于2.66×10~(-6)s~(-1);富含Ce、La、Nd等稀土元素的共晶β相和蠕变期间动态沉淀产生的晶界强化及沉淀强化是该合金的主要强化机制,而孪晶切变和共晶β相开裂致使其高温蠕变抗力显著降低。     

Effects of hot isostatic pressing and heat treatment on cast cobalt alloy

Investment cast biomedical alloys are often heat treated to refine the microstructure and improve mechanical properties. Test specimens of American Society for Testing and Materials F75 alloy (Co–28 wt-%Cr–6 wt-%Mo) were cast and solidified at two cooling rates, which influenced the size and area fraction of secondary phases (carbides) precipitated at grain boundaries and in interdendritic zones. The specimens were then subjected to hot isostatic pressing and age hardening. This produced smaller globular carbides of reduced area fraction, and reduced the size of micropores, independent of as cast characteristics. Strength and hardness were not significantly altered. The most significant effect of the post-casting treatment was to increase the ductility of the alloy, most likely due to the dissolution of brittle intergranular carbides and reduction in pore size.     

微弧氧化对镁合金摩擦及胶接性能的影响

为解决镁合金表面耐摩擦和胶接性能较差的问题,采用微弧氧化法在MB15镁合金原位生长微弧氧化膜层.利用X射线衍射、扫描电镜、摩擦磨损试验机和万能拉伸实验机对膜层的结构组成、表面形貌、摩擦性能和胶接性能进行了研究.结果表明：MB15镁合金表面微弧氧化后可以形成均匀多孔的陶瓷涂层,膜层由MgO和MgAl2O4组成,经微弧氧化...     

The structure of a cast dental Ni-Cr-Be alloy

The structure of a typical dental Ni-Cr-Be alloy with 1.8 wt% Be has been investigated by SEM and TEM as well as by quantitative X-ray microanalyses in both instruments. Due to its low atomic weight the atomic fraction of Be is as high as 0.10. During solidification beryllium segregates substantially, and a large volume fraction of the casting is made up of a eutectic with coarse ( 1 µm diameter) alternating rods of fcc Ni-Cr and NiBe with a CsCl-type structure (ordered bcc). Smaller ( 0.1 µm diameter) rods of NiBe are precipitated in matrix in the solid state. Microanalyses of the NiBe rods show that they have a low chromium content ( 1.5 wt%). The cube boundary planes of the ordered b cc and fcc structures have a slight difference in orientation of about 7° which is most probably due to a small coherency misfit of the two types of lattices. The 100 directions in cube boundary plane of the fcc structure are nearly parallel to the 110 directions of the ordered bcc cube boundary plane. Sometimes another and more complex relationship between the two lattices occurs. The alloy contains 3.9 wt% Al which gives rise to numerous small ( 10 nm), spherical, ordered particles of Ni₃Al both in matrix as well as in the fcc eutectic rods.     

Age hardening and precipitation in a cast magnesium-rare-earth alloy

The precipitation sequence responsible for the age-hardening behaviour of a cast Mg-1.3 wt% rare-earth alloy has been investigated by analytical electron microscopy. Very fine intermediate precipitates formed at an early stage of ageing. Plate-shaped Mg₃MM precipitates (MM = misch metal) and hexagonal prism-shaped Mg₁₂MM precipitates were primarily responsible for age hardening. Precipitate morphologies, crystal structures and crystallographic orientation relationship were determined for the various types of precipitates that formed during ageing at different temperatures.     

Superhardness of cast iron induced by copper under laser treatment

A new phenomenon has been observed, i.e., the copper-induced formation of superhard cast iron having a microhardness up to 22 000 MPa as a result of cw laser treatment of the surface of gray iron covered with a thin copper inductor layer. The induction phenomenon involves the inductor in close contact with the crystal structure specifically influencing the phase transition processes which take place in the surface layers of metals and alloys during cooling after laser treatment. Pis’ma Zh. Tekh. Fiz. 25, 61–65 (December 26, 1999)     

Microstructure characteristics and mechanical properties of laser weld bonding of magnesium alloy to aluminum alloy

Weldability of magnesium alloy to aluminum alloy in laser weld bonded (LWB) joints was investigated. Results showed that magnesium/aluminum could be easily joined by LWB under proper technological parameters. The weld was characterized by complex vortex flow at the bottom, and there existed intermetallic compound layer between weld pool and lower sheet metal, which was composed of the brittle phases of Al₃Mg₂ and Al₁₂Mg₁₇, resulting in the formation of weld cracking. Adhesive in the weld was heated up and then escaped in the form of gas, which would not affect the microstructures of weld. However, Adhesive near the weld was oxidized and carbonized, leading to the formation of a failure zone. But this failure zone had little influence on load bearing capability of the joints. Besides, it was also found that the penetration of LWB joints was greater than that of laser welded joints alone. In tensile shear test and T-peel test, LWB samples gave both the highest shear resistance and the highest peel resistance compared to laser welded samples and adhesive bonded samples.     

一种新型高强韧铸造铝硅合金(ZL120)热处理工艺的研究

对一种新型高强韧铸造铝硅合金 (暂名ZL1 2 0 )的T6热处理工艺进行了研究 .对固溶温度Ts、固溶时间ts、时效温度Ta和时效时间ta进行三水平正交试验 ,并测试了该合金在对应处理状态下的力学性能 ,然后根据此结果再进行验证性试验 .结果表明 ,改变这四个参数可得到一系列的性能组合 ,例如 ,热处理工艺为 5 2 0℃× 1 6h+ 60℃水冷 + 1 70℃ × 8h时 ,可获得抗拉强度σb ≥ 40 0MPa和延伸率δ5 ≥ 3 %的力学性能 .     

Ageing characteristics of cast Zn-Al based alloy (ZnAl7Cu3)

Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich phase and four phase transformation, + T + , were detected during ageing at 150°C. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich and phases.