Improved Fatigue Behavior of Pipeline Steel Welded Joint by Surface Mechanical Attrition Treatment(SMAT)

A pipeline steel X80 with welded joint was subjected to surface mechanical attrition treatment （SMAT）. After SMAT, a nanostructure surface layer with an average grain size of about 10 nm was formed in the treated sample, and the fatigue limit of the welded joint was elevated by about 13% relative to the untreated joints. In the low and the high amplitude stress regimes, both fatigue strength and fatigue life were enhanced. Formation of the nanostructured surface layer played more important role in the enhanced fatigue behavior than that of residual stress induced by the SMAT.

Study on the friction and wear properties of the surface nanocrystallized 1.0C-1.5Cr steel induced by the surface mechanical attrition treatment

Nano-structured layers are fabricated on the surface of 1.0C-1.5Cr steel by using the surface mechanical attrition treatment(SMAT)technology,and the microstructures of the surface nano-crystallization layers are characterized by means of X-ray diffraction(XRD)and transmission electron microscopy(TEM).The friction and wear properties are also investigated by a UMT-2 friction and wear tester.Experimental research has indicated that the average diameter of nanocrystalline grains in the surface layer after being treated for 15 min is in the range of 10-20 nm,and ferrite and cementite grains can not be identified by their morphologies.The wear-resistance of the specimen treated for 15 min has been doubled,compared with that of the matrix due to the grain refinement to a nano-sized scale.The lowest friction coefficient is 0.27,which is for the specimen treated for 30 min,resulting from the dissolution of the cementite phase and the formation of a relative homogenous structure.The SMAT technique for enhancing the wear-resistance of the 1.0C-1.5Cr steel has an optimum processing time,which is in the range of 15-30 min.The dominant wear mechanism of the specimen treated for 15 min changes from adhesive wear into particle wear.

Nickel-based superalloy architectures with surface mechanical attrition treatment: Compressive properties and collapse behaviour

Surface modifications can introduce natural gradients or structural hierarchy into human-made microlattices,making them simultaneously strong and tough.Herein,we describe our investigations of the mechanical properties and the underlying mechanisms of additively manufactured nickel–chromium superalloy(IN625)microlattices after surface mechanical attrition treatment(SMAT).Our results demonstrated that SMAT increased the yielding strength of these microlattices by more than 64.71%and also triggered a transition in their mechanical behaviour.Two primary failure modes were distinguished:weak global deformation,and layer-by-layer collapse,with the latter enhanced by SMAT.The significantly improved mechanical performance was attributable to the ultrafine and hard graded-nanograin layer induced by SMAT,which effectively leveraged the material and structural effects.These results were further validated by finite element analysis.This work provides insight into collapse behaviour and should facilitate the design of ultralight yet buckling-resistant cellular materials.

Effect of Surface Mechanical Attrition Treatment on Corrosion Behavior of 316 Stainless Steel

The nanocrystalline microstructure of the surface of 316 stainless steel （316SS） induced by surface mechanical attrition treatment （SMAT） was determined by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The technique of hydrogen embrittlement was first used to obtain the information of the brittleness cleavage plane. The effects of SMAT and the following annealing process on the corrosion behavior of 316SS were investiga- ted by potentiodynamic polarization curves and potentiostatic critical pitting temperature measurements. The results demonstrated that the nanoerystalline layer with an average grain size of 19 nm was produced. However, there were lots of cracks on the surface, which led to the degradation in the corrosion resistance of 316SS after SMAT. Never- theless, after annealing treatment, the corrosion resistance of the nanocrystalline surface had been improved greatly. The higher the annealing temperature, the better was the corrosion resistance.

Strain-induced Microstructure Refinement in a Tool Steel Subjected to Surface Mechanical Attrition Treatment

A nanostructured surface layer has been fabricated on an AISI H13 tool steel by means of surface mechanical attrition treatment （SMAT）.Strain-induced refinement processes of ferrite grains and carbide particles have been investigated by transmission electron microscopy （TEM） and scanning electron microscopy （SEM） in the SMAT surface layer.Grain refinement of ferrite is found to be dominated by dislocation activities and greatly facilitated by a large number of carbide particles at a depth 〉20 μm.The comparisons with microstructure refinement processes in other SMAT ferrite steels indicate that a larger volume fraction of carbide particles with a lower shear strength is expected to facilitate the refinement process of ferrite grains.

Thermal Stability of Nanocrystalline AZ31 Magnesium Alloy Fabricated by Surface Mechanical Attrition Treatment

A nanocrystalline layer （NL） was fabricated on the surface of AZ31 magnesium （Mg） alloy sheet by surface mechanical attrition treatment （SMAT）. The microstructure of the Mg alloy was characterized by optical microscopy, X-ray diffraction and microhardness test. The results showed that both the microstructure and microhardness of AZ31 Mg alloy sheet after SMAT revealed a gradient distribution along depth from surface to center. The thermal stability of the NL was investigated through characterizing the microstructure evolution during the post-isothermal annealing treatment within the temperature range from 150 to 250℃. The NL exhibits a certain degree of thermal stability below 150 ℃, while it disappears quickly when annealing at the temperature range of 200-250 ℃. The grain growth kinetics of the nanocrystalline of AZ31 Mg alloy induced by SMAT was investigated. The activation energy of nanocrystalline AZ31 Mg alloy was obtained with a value of 92.8 kJ/mol.

The Portevin-Le Chatelier effect of gradient nanostructured 5182 aluminum alloy by surface mechanical attrition treatment

Nanocrystalline surface layers and gradient nanostructure in 5182 aluminum alloy have been produced through surface mechanical attrition treatment(SMAT). The results indicate that the gradient nanostructure can not only improve the mechanical properties of 5182 Al alloy, but also has a certain effect on the Portevin-Le Chatelier(PLC) effect. The yield and ultimate tensile strength of 5182 Al alloy with SMAT are significantly improved combining with the decrease of fracture elongation compared with the as-received one. The PLC effect of 5182 Al alloy could be effectively postponed by the formation of gradient nanostructure after SMAT. It leads to the increase of critical strain of the PLC effect, more concentrated distribution of serrated strain, and increase of average stress amplitude in special strain range. The influence of grain size and gradient nanostructure on the PLC effect of 5182 Al alloy was also discussed in detail. Grain refinement could sharply increase the density of dislocations and hinder the movement of dislocations, which results in the decrease of moving speed of dislocations and the more concentrated distribution of solute atoms. The solute atoms would aggregate to form nano precipitates and further impede movement of dislocation. The stronger interaction between the dislocations and the nano precipitates is the main mechanism of postponed PLC effect.

利用SMAT和SPS在纯铁表面制备铁镍合金层

利用放电等离子烧结(SPS)技术实现了镍粉在纯铁表面铁镍合金层的制备,通过纯铁表面机械研磨(SMAT)的预处理获得表面纳米层和梯度结构有效促进了铁镍的扩散,提升了合金层厚度和结合强度。通过XRD、SEM、EDS、硬度和摩擦磨损实验等,表征铁镍合金层形貌、组成,测试了力学性能。结果表明:纯铁试样经过SMAT预处理和SPS后,在表面获得了约50μm的铁镍合金层,沿着深度方向镍元素含量梯度变化,而在未经SMAT预处理的纯铁表面仅有25μm的合金层,本方法实现了合金层厚度明显增加。SMAT预处理后的SPS试样硬度提升,表面磨损量和犁沟槽深度减少,结合力增强,耐磨性提升明显。

Effect of surface mechanical attrition treatment of titanium using alumina balls： surface roughness, contact angle and apatite forming ability

The effect of surface mechanical attrition treatment （SMAT） of commercially pure titanium （CP-Ti） using 8 mm O alumina balls was studied. SMAT induced plastic deformation, increased the surface roughness, reduced the grain size and decreased the contact angle （from 64° to 43°） with a corresponding increase in surface energy （from 32 to 53 mJ/m2）. Untreated CP-Ti and those treateded using alumina bails for 900 s reveals no apatite growth until the 28th day of immersion whereas those treated for 1800 and 2700 s exhibit apatite growth In selective areas and the extent of growth is increased with increase in immersion time an SBF; The study reveals that SMAT using alumina balls is beneficial in imparting the desired surface Cheracteristics, provided the surface contamination is limited, which would otherwise decrease the apatite forming ability.

Effect of Surface Mechanical Attrition Treatment on Tribological Behavior of the AZ31 Alloy

By surface mechanical attrition treatment（SMAT）,a gradient nano structure（GNS） from the surface to center was generated in the AZ31 alloy sheet.The tribological behavior of AZ31 alloy with GNS was systematically investigated by using dry sliding tests,a 3D surface profile-meter and a scanning electron microscope equipped with an energy-dispersive spectrometer.The experimental results indicate that the Mg alloy with GNS exhibits better wear resistance comparing to the as-received sample,which is associated to the alteration of wear mechanism at different sliding speeds.The Mg alloy with GNS presents the wear mechanism of the abrasive wear at 0.05 m/s and the oxidative wear at 0.5 m/s,respectively.Moreover,the GNS can effectively promote the reaction between the oxygen and worn surface,which leads to a compact oxidation layer at 0.5 m/s.The effect of oxidation layer on the wear resistance of the Mg alloy was also discussed.

Serrated plastic flow behavior and microstructure in a Zr-based bulk metallic glass processed by surface mechanical attrition treatment

The serrated plastic flow,microstructure and residual stress of a Zr_（55）Cu_（30）Ni_5Al_（10） bulk metallic glass（BMG）undergone surface mechanical attrition treatment（SMAT）have been investigated by a combination of compression tests with scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）and the incremental hole-drilling strain-gage method.It is found that SMAT leads to various microstructural modifications and residual stress distribution in the surface layers of the Zrbased BMG due to the mechanically-induced nanocrystallization and generation of shear bands.As a result,the BMG alloy exhibits a remarkable work-hardening like behavior and significant increase of plastic strain from less than 1%to 15%,and its plastic deformation dynamics yields a power-law distribution of shear avalanches.Based upon the analysis of the experimental results,it is indicated that this can be connected to the SMAT-induced microstructural modifications and the resulting residual compressive stress in the Zr-based BMG.

Deformation mechanism and dynamic precipitation in a Mg-7Al-2Sn alloy processed by surface mechanical attrition treatment

The effect of second phases on the deformation mechanism of as-cast, solution-treated and aged Mg-7Al-2Sn (AT72) alloys during surface mechanical attrition treatment (SMAT) was investigated. Twinning was suppressed in the alloys containing second phases, which can provide nonuniform microstructures and phase boundaries as dislocation sources. Dynamic precipitation in AT72 alloys was studied during SMAT deformation as well.Mg2Sn particles can dynamically precipitate on the surface of all AT72 alloys during SMAT process. The quantity of Mg2Sn particles in the as-cast alloy, which is determined by the initial quantity of second phases, is larger than that of T4 and T6 alloys after the SMAT process.

表面纳米化对低碳钢耐腐蚀性能的影响及机制

采用表面机械研磨(SMAT)处理低碳钢材料,实现表面纳米化,探讨了表面纳米化对低碳钢耐腐蚀性的影响。结果表明,表面纳米化作用下,碳含量较低的低碳钢材料表面塑性变形较强烈,表面X射线衍射峰宽化较明显;对不同碳含量低碳钢进行表面纳米化处理,碳含量越低,处理后表面粗糙度越大、耐腐蚀性能越差。

Effect of mechanical attrition on microstructure and properties of electro-deposition coatings on NdFeB

Surface mechanical attrition treatment （SMAT） was developed to synthesize nanostructure coatings on alloy surface. The SMAT action was applied in the process of Ni and Cu electroplating coatings on NdFeB substrates in this paper. The role of mechanical attrition during barrel plating on the microstructure, mechanical and corrosion resistant properties of the coatings was exam- ined. The scanning electron microscopy （SEM） observation showed that the mechanical attrition could refine grain size, markedly smooth the coating surface and obviously decrease the number of pore in the coatings. The continuous collisions of glass balls onto the NdFeB samples could induce more beneficial nucleation defects on the coating, which was helpful for increasing nucleation sites and the nucleation rate. The mechanical attrition could also restrain the heterogeneous growth of the coating grain tips due to the abra- sive action of stainless steel balls. The Tafel polarization curve experimental results indicated that SMAT process could enhance the corrosion resistance of coatings on NdFeB. The scratching test revealed that the binding force between coating and NdFeB substrate could be improved dramatically with SMAT process.

Formation mechanism and wear behavior of gradient nanostructured Inconel 625 alloy

The formation mechanism and wear behavior of a gradient nanostructured(GNS) Inconel 625 alloy were investigated using SEM, TEM and ball-on-disc sliding wear tester. The results show that surface mechanical grinding treatment(SMGT) induced an approximately 800 μm-deep gradient microstructure, consisting of surface nano-grained,nano-laminated, nano-twined, and severely deformed layers, which resulted in a reduced gradient in micro-hardness from 6.95 GPa(topmost surface) to 2.77 GPa(coarse-grained matrix). The nano-grained layer resulted from the formation of high-density nano-twins and subsequent interaction between nano-twins and dislocations. The width and depth of the wear scar, wear loss volume, and wear rate of the SMGT-treated sample were smaller than those of untreated coarse-grained sample. Moreover, the wear mechanisms for both samples were mainly abrasive wear and adhesive wear, accompanied with mild oxidation wear. The notable wear resistance enhancement of the GNS Inconel 625 alloy was attributed to the high micro-hardness, high residual compressive stress, and high strain capacity of the GNS surface layer.

Influence of Surface Nano-structured Treatment on Pack Boriding of H13 Steel

In order to lower the boriding temperature of hot work steel H13, method of surface mechanical attrition treatment （SMAT）, which can make the grain size of the surface reach nano-scale, was used before pack boriding. The growth of the boride layer was studied in a function of boriding temperature and time. By TEM （transmission electron microscopy）, SEM （scanning electron microscopy）, XRD （x-ray diffraction） and microhardness tests, the grain size, thermal stability of the nano-structured （NS） surface and the thickness,appearance, phases of the surface boride layer were studied. Kinetic of boriding was compared between untreated samples and treated samples. Results showed that after SMAT, the boride layer was thicker and the hardness gradient was smoother. Furthermore, after boriding at a low temperature of 700℃ for 8 h, a boride layer of about 5 μm formed on the NS surface. This layer was toothlike and wedged into the substrate, which made the surface layer combine well with the substrate. The phase of the boride layer was Fe2B. Research on boriding kinetics indicated that the activation energy was decreased for the treated samples.

预制表面梯度应变层增强高铁制动盘的耐磨性能

随着客运铁路高速化,列车制动盘的磨损日益加剧,严重威胁列车服役的安全性。为了提高低碳马氏体钢制动盘的耐磨性,采用表面机械研磨处理(SMAT)技术在材料表面制备梯度组织,进而延长材料的服役寿命。结果表明:经SMAT处理后,样品表面形成厚约180μm的梯度应变层,切应变沿深度呈梯度分布。板条马氏体被挤压成塑性流线,在最表层形成亚微米晶和条状结构。微米划痕试验发现,样品表层材料的硬化率和摩擦性能随着深度呈梯度变化,耐磨性相比基体增强了1.2倍。在循环应力作用下,靠近样品表面的马氏体晶粒被细化,最表层材料的位错密度比基体提高了14.6倍,从而提高了制动盘钢的表面硬度和耐磨性。此外,与其他铁路耐磨材料相比,样品表现出较高的应变硬化速率。研究成果可为制动盘梯度应变层的工程应用提供参考。

液氮环境下表面机械研磨处理对纯铜的影响

使用表面机械研磨处理(surface mechanical attrition treatment,SMAT)在液氮环境中分别对退火态铜板进行30、60 s及120 s的加工处理.通过对样品进行准静态拉伸测试发现SMAT样品的屈服强度相较于退火态纯铜均提升了2-5倍,其中SMAT 60 s样品的屈服强度相比于退火态纯铜提高了211.3%,而其均匀延伸率仍可保持在24.6%.结合硬度测试和金相观察,发现处理过后的样品从表面到芯部形成了明显的梯度结构.综合结果表明在60 s SMAT处理后的样品具有最佳的强度-延展性匹配关系.

Enhanced initial biodegradation resistance of the biomedical Mg-Cu alloy by surface nanomodification

Mg-Cu alloys are promising antibacterial implant materials.However,their clinical applications have been impeded by their high initial biodegradation rate,which can be alleviated using nanotechnology by for example surface nanomodification to obtain a gradient nanostructured surface layer.The present work(i)produced a gradient nanostructured surface layer with a∼500µm thickness on a Mg-0.2 Cu alloy by a surface mechanical grinding treatment(SMGT),and(ii)studied the biodegradation behavior in Hank's solution.The initial biodegradation rate of the SMGTed samples was significantly lower than that of the unSMGTed original counterparts,which was attributed to the surface nanocrystallization,and the fragmentation and re-dissolution of Mg_(2)Cu particles in the surface of the SMGTed Mg-0.2 Cu alloy.Furthermore,the SMGTed Mg-0.2 Cu alloy had good antibacterial efficacy.This work creatively used SMGT technology to produce a high-performance Mg alloy implant material.

表面机械研磨诱导AISI 304不锈钢表层纳米化 Ⅰ.组织与性能

采用表面机械研磨处理(SMAT)在AISI 304不锈钢上制备出纳米结构表层,研究纳米化行为及其对硬度的影响。结果表明:经过SMAT后,样品表面形成了厚度约为30μm的纳米晶层,显微组织由平均晶粒尺寸约为10nm的单一马氏体相演变为尺寸稍大的双相组织;在距表面30—300μm的范围内,显微组织由以亚微米级的奥氏体多系孪晶为主逐渐演变为单系孪晶,表面纳米化是晶粒碎化与纳米尺度新相形成共同作用的结果,与心部相比,表面硬度显著提高。