Surface nanostructures in commercial pure Ti induced by high energy shot peening

The high-energy shot peening (HESP) technique was used to obtain the surface nanocrystalline microstructure for a hcp metal titanium. XRD, SEM and TEM were applied to characterize the microstructure of the surface layer. Large amount of the deformation twins in the surface layer were observed by SEM in the specimens after HESP treatment in a shot-time, and the number of deformation twins both in a single plane and in intersecting planes increases with HESP time, until the twin character disappears completely in the top surface layer, which means that the severe plastic deformation(SPD) occurs on the surface. The XRD analysis results show that after HESP treatmen for 30 - 60 min the surface grain size decreases to nanoscale. According to the TEM images and corresponding diffraction patterns from SPD areas of the 120 min-treatment specimen, the measured grain size near the surface is about 20 - 30 nm. The grain size in deformation layer increases with the depth from the surface, and the nanostructured layer is about 20 μm in depth. Therefore, the surface nanocrystalline and a gradient microstructure from the surface to the matrix are obtained, which results in the micro-hardness decreasing from surface to the matrix gradually.     

工业纯钛喷丸强化研究

采用TEM结合SEM和XRD对工业纯钛喷丸强化后显微组织结构、断口形貌、残余应力进行分析,研究了影响疲劳性能的3个因素即：组织、应力、粗糙度。结果表现：孪生是六方合金的塑性变形主要形式,喷丸强化表层形变组织由孪晶和变形带构成,表层孪晶间强烈交互作用,可造成显微损伤;表层残余应力在疲劳后发生明显松驰,有益贡献也相应的降低;表面粗糙度提高,具有负的影响。     

The Effect of Shot Peening on the Fatigue Strength of Pure Titanium

The changes of the substructure, the residual stress and the surface roughness of shot peened pure titanium were analyzed by means of SEM, TEM, XRD and surface roughness measurements in this paper. The results show that shot peening increased the fatigue strength of pure titanium. The substructures of shot peened pure titanium consist of dislocations, deformation twins and deformation bands. Fatigue loading will relax the compressive residual stress and decrease the strengthening effect. The increased surface roughness has negative effects.     

Microstructure characteristics of as-surface nanocrystallized 1420 aluminum alloy by high-energy shot peening

A nanostructured surface layer was fabricated on 1420 aluminum alloy by high-energy shot peening.Microstructures were characterized by X-ray diffractometer (XRD), transmission electron microscope (TEM) and high-resolution electron microscope(HRTEM), and microhardness measurement was conducted along the depth from top surface layer to matrix of the sample peened for 30 rain. The results show that a nanocrystalline layer about 20μm in thickness is formed on the surface of the sample after high-energy shot peening, in which the grain size is changed from about 20 nm to 100 nm. In the surface layer of 20-50μm in depth, the microstructure consists of submicron grains. The surface nanocrystallization is accomplished by dislocation slip. The microhardness of the top surface nanostructured layer is enhanced obviously after high-energy shot peening(HESP) compared with that of the coarse-grained matrix.     

SS400钢焊接接头表层组织纳米均一化及硬度均一化处理

采用高能喷丸技术以SS400钢焊接接头的表面层进行处理。利用XRD,TEM,SEM对处理后的表面层进行结构表征,同时测量了高能喷丸引起的硬度变化。结果表明,高能喷丸处理可使焊接接头的表面层形成尺寸均匀、取向随机分布的纳米晶;焊接接头三个区域的纳米层硬度一致,且远高于高能喷丸处理前样品的硬度,实现了SS400钢焊接接头区表层组织纳米均一化和硬度均一化。表面纳米化对材料表面的强化有着重要的贡献。     

A numerical model of severe shot peening (SSP) to predict the generation of a nanostructured surface layer of material

Generation of a surface layer of material characterized by grains with dimensions up to 100 nm by means of severe plastic deformation is one of the most interesting methods to improve the mechanical behaviour of materials and structural elements. Among the ways to obtain a surface layer with this characteristic, shot peening is one of the most promising processes, since it is applicable to very general geometries and to all metals and metal alloys without high-tech equipments. Notwithstanding the fact that the ability of shot peening to obtain nanostructured surfaces by using particular process parameters (mainly high impact energy and long exposure time) is proved, deep knowledge of the correct choice of quantitative values of process parameters and their relation to the grain size and the thickness and uniformity of the nanostructured layer is still lacking.In this paper a finite element model of severe shot peening (SSP) is developed with the aim of predicting the treatment conditions that lead to surface nanocrystallization. After having assessed the accuracy of the model as regards mesh parameters and constitutive law of the material, the results are discussed and interpreted in terms of induced residual stresses and surface work hardening. A method to assess the formation of nanostructured layer of materials based on the value of the equivalent plastic strain is developed.The comparison with experimental results allow to affirm that the model is a useful tool to predict the generation of a nanostructured surface layer by shot peening and to relate the peening parameters with the treated surface layer in terms of residual stresses, work hardening, and depth of the nanostructured layer.     

表面强化对工业纯钛显微组织的影响

工业纯钛经喷丸,滚压强化后,疲劳强度得到不同程度的提高,逐层TEM亚结构对比分析结果表明,工业纯钛疲劳强度的提高和强化层组织中孪晶的形成有关,工业纯钛疲劳前后组织中主要是位错数量的变化,而强化试样疲劳前后组织的结构既有位错,孪晶数量的变化,又有孪晶－晶界,孪晶－孪晶之间的交互作用,喷丸较滚压强化效果显著的部分原因是表层形成了准孪晶栅栏。     

高能喷丸表面纳米化对工业纯钛组织性能的影响

用高能振动喷丸法对工业纯钛进行了表面纳米化的研究。用X 射线衍射、光镜和透射电镜对表层变形层金相组织、晶粒尺寸、显微硬度进行分析。结果表明 ,具有密排六方晶体结构的工业纯钛经高能喷丸处理后 ,在表面可以形成具有一定厚度的纳米晶粒组织 ;随着高能喷丸时间的增加 ,表面层的晶粒尺寸变小 ,而表面硬度提高。     

7050铝合金表面亚微米化及其显微硬度的研究

通过改进7050铝合金表面纳米化技术(调节喷丸压力、弹丸直径和喷丸时间)在材料表面获得亚微米晶层,利用OM、XRD、SEM等方法对亚微米结构表层进行了观察和分析。结果表明:喷丸使7050铝合金表面发生一定的塑性变形,表层亚微米晶尺寸约88 nm,显微硬度比基体提高2倍。     

ITER级CuCrZr合金高能喷丸后的组织与强化机制

用X射线衍射仪、扫描电子显微镜、透射电子显微镜、显微硬度仪对经喷丸处理的Cu-0.8Cr-0.1Zr合金进行组织结构分析和硬化效果的测试,并在此基础上探讨了合金喷丸强化机制。结果表明,合金喷丸后在距表层300μm深度内形成了剧烈变形层和变形层两种不同变形程度的区域。其中剧烈变形层内位错密度较高,并形成位错胞亚结构和孪晶亚结构。随喷丸时间的增加,剧烈变形层晶粒尺寸可细化至80nm,表层HV硬度达到1.99GPa,较未变形试样提高1倍以上。合金的喷丸强化机制为细晶强化和应变硬化,而应变硬化的贡献大于细晶强化。     

纯铁表面喷丸处理对镍扩散性能的影响

采用高能喷丸(HESP)对纯铁棒样端面进行了表面自纳米化(SSNC)处理,通过金相显微镜、扫描电子显微镜及x射线衍射对表面变形层厚度、晶粒度及硬度等进行了表征;然后在Gleeble 1500型热模拟试验机上实现镍箔在纯铁表面的渗入,并利用扫描电子显微镜对扩散的效果进行了比较分析.结果表明,工业纯铁经喷丸处理,表面晶粒得...     

高能喷丸处理对Al-Zn-Mg合金的组织和力学性能的影响

采用透射电镜(TEM)、光学显微镜(OM)、显微硬度计和微力材料试验机等研究了Al-Zn-Mg合金高能喷丸处理后的表层显微组织和力学性能。结果表明:经高能喷丸处理后,在距离Al-Zn-Mg合金表面约20μm深度范围内形成了随机取向的等轴纳米晶层,表面层的结构特征尺寸随层深的增大呈梯度变化,无明显界面;由于细晶强化作用和合金化层的形成,Al-Zn-Mg合金的表面硬度为基体的3倍以上,硬度随距表面距离的增加而逐渐减小;Al-Zn-Mg合金的整体屈服强度亦显著提高,且形变速率越大,屈服强度越高,这主要是由于变形过程中位错塞积强化、多晶体的细晶强化和加工硬化的共同作用导致的。     

Zr-4合金表面变形纳米结构TEM研究

利用透射电镜对Zr-4合金表面进行高能喷丸处理所致纳米结构的微观组织演变特征进行了研究.结果表明,经过喷丸处理变形后,Zr-4合金表面形成一层平均晶粒尺寸为几纳米至十几纳米的致密纳米层,随着离表面距离的增加,晶粒尺寸也不断增加.通过对Zr-4合金的变形行为以及微观结构组织演变的观察和分析,探讨了纳米晶的形成机制.     

表面纳米化对SS400钢应力腐蚀性能的影响

采用高能喷丸技术对SS400钢表面进行纳米化处理,利用透射电子显微镜分析了表面纳米晶层的结构特征,同时对高能喷丸表面纳米化处理后残余应力沿厚度方向的变化进行了分析.结果表明:经过超声冲击处理后,试样表层的晶粒可细化至纳米尺度,且在表面形成厚度约为600 μm的压应力层,压应力沿试样深度方向逐渐减小直至过渡到拉应力.在98±3℃温度下,Ca(NO3)2 57%+NH4NO3 3%溶液中进行的慢应变速率拉伸试验,结果表明,高能喷丸表面纳米化可以提高SS400钢的抗应力腐蚀开裂(SCC)性能.     

喷丸强度对FGH4113A高温合金微观组织的影响及定量表征

镍基粉末高温合金涡轮盘长期在高温高应力条件下服役,对其综合力学性能有着严苛的要求,而表面形貌与微观组织对盘件性能有着至关重要的影响,通常需进行表面喷丸强化处理。基于此,本工作系统性地研究了不同喷丸强度下FGH4113A合金的表面和亚表层微观组织及变形情况,并探究了两者的定量关系。结果表明：经过喷丸处理后,合金亚表面产生位错塞积,诱发晶粒内形成变形孪晶,并且变形孪晶数量随喷丸强度的增大而增大。另外,喷丸强化引入的位错使变形层存在大量的小角晶界,从而发生晶粒细化提升了合金硬化效果。随着喷丸强度的增大,合金表面粗糙度、表面残余压应力、硬化层厚度以及表面显微硬度等特征呈现出不断增大的趋势。这些研究结果可为实际生产过程中喷丸强化参数的调控提供一定的数据支撑。     

喷丸工艺对TC4钛合金梯度纳米晶结构的作用规律

目的通过改变喷丸的压力或时间,在钛合金表面制备出剧烈塑性变形(SPD)层较厚、硬度较高的梯度纳米晶结构。方法改变喷丸压力(0.3~0.6 MPa)或喷丸时间(15~60 min),调控TC4钛合金表面梯度纳米晶结构的变形层厚度和纳米晶晶粒尺寸。利用金相显微镜观察塑性变形层截面的组织形貌,通过X射线衍射仪(XRD)和透射电子显微镜(TEM)确定喷丸表面纳米晶的晶粒尺寸,通过显微硬度计对塑性变形层的截面硬度进行研究。结果一定喷丸压力(0.6MPa)下,SPD层和总变形层厚度分别在喷丸25、30 min时达到饱和值78μm和143μm。一定喷丸时间(25 min)下,SPD层和总变形层的厚度随喷丸压力的增加而增厚,在0.4 MPa时达到饱和,分别为78μm和120μm。当SPD层厚度进入饱和阶段后,表层晶粒大小和硬度强化程度都趋于稳定;在0.6 MPa下,当表面α相细化至稳定阶段时,晶粒尺寸为30~90 nm,表面硬度提高约30%。结论喷丸SPD层及总变形层的厚度随喷丸时间的延长或喷丸压力的增大而增厚,当SPD层厚度趋于饱和后,表面晶粒尺寸和硬度强化程度都已饱和。     

Microstructure evolution ofAZ91D induced by high energy shot peening

A nanostructured surface layer was fabricated on a AZ91D magnesium alloy by using a high-energy shot peening（HESP）. HESP induced structure along the depth of the treated sample surface layer was characterized by means of X-ray diffractometer （XRD）, transmission electron microscope（TEM） and high resolution transmission electron microscopc（HRTEM）. The experimental results show that a deformed layer of about 50 μm has formed after HESP treatment and the average grain size increases from about 40 nm in the surface layer to about 200 nm at the depth of 40 μm. The surface nanocrystallization can realize intercoordination of the dislocations slipping and dynamic recrystallization. The nanocrystalline grains have stacking faults and dislocation in their interiors. The microhardness of the top surface is about triplicate that of the coarse-grained matrix.     

SHOT-PEENING STRENGTHENED LAYER AND ITS EFFECT ON FATIGUE STRENGTH OF α-BRASS

In shot peened α-brass surface layer{111} type planar defects and deformation microtwinshave been observed by means of TEM analysis.The density of microtwins deereases with theincrease of layer depth.The enhancement of fatigue strength and the unrelaxation of residualstress after shot peening are concerned in the substructures of strengthened layer.     

喷丸处理实现纯钛表面纳米化的研究

利用喷丸处理技术实现了工业纯钛的表面纳米化,利用光学显微镜（OM）、扫描电镜（SEM）和透射电镜（TEM）对表层组织演变过程和表层晶粒纳米化的细化机理进行了研究,并用显微硬度计对表层硬度进行了测试。研究结果表明,传统表面喷丸处理后可在工业纯钛表面得到一定厚度的纳米层和剧烈塑性变形层。喷丸处理后,工业纯钛表面硬度显著提高。     

内壁喷丸处理对TP304H耐热钢锅炉管抗水蒸汽氧化性能的影响

将经表面喷丸处理和未处理的TP304H钢管安装于锅炉再热器的高温段运行7474h后,对内壁氧化膜进行形貌观察、能谱分析和X射线衍射分析。结果表明,喷丸处理可大幅度提高TP304H钢的抗水蒸汽氧化性能,氧化膜的生长速率显著降低且氧化膜的粘附性提高。显微分析表明,氧化膜由双层结构转变为单一高Cr氧化膜层,外层Fe的氧化层消失。分析认为喷丸在管子内壁产生的剧烈形变引起晶粒细化和马氏体相变,在高温下促进了Cr向表面扩散及生成富Cr的氧化层。