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.     

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。     

表面纳米化对AZ91D镁合金渗铝行为的影响

镁合金表面渗铝是提高耐蚀性的一种有效方法。本研究将表面纳米化作为渗铝的预处理过程。采用高能喷丸对AZ91D镁合金进行表面纳米化处理,然后进行真空铝扩散得到渗铝层。用透射电镜(TEM)和扫描电镜(SEM)观察了渗铝层的形貌。结果表明,在对AZ91D镁合金表面高能喷丸后获得了100 nm的晶粒尺寸。在高能喷丸之后,渗铝层的深度比未高能喷丸的渗铝层厚。在440℃下扩散12 h后,渗铝层的深度增加到70μm。采用电化学方法对AZ91D镁合金的耐腐蚀性能进行了表征。结果表明,渗铝层明显降低了AZ91D镁合金的腐蚀速率。因此,高能喷丸强化有利于镁合金表面渗铝,提高镁合金的耐蚀性。     

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.     

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.     

表面纳米化对SS400钢焊接接头应力腐蚀性能的影响

采用高能喷丸技术在SS400钢焊接接头表面层上制备纳米结构,利用透射电子显微镜分析研究了表面纳米晶层的结构特征,并利用XRD对高能喷丸表面纳米化处理后表面层残余应力进行了分析.同时,应用慢应变速率拉伸试验研究了SS400钢焊接接头在敏感腐蚀介质硝酸盐溶液(98℃±3℃温度下,57%Ca(NO3)2+3%NH4NO3)中的应力腐蚀(SCC)行为.结果表明,经过高能喷丸处理后,试样表层的晶粒可细化至大约10 nm,且在表面形成残余压应力;高能喷丸表面纳米化可以提高SS400钢焊接接头抗硝酸盐溶液SCC性能.     

Thermal stability of nanocrystalline in surface layer of magnesium alloy AZ91D

Isothermal and isochronal annealing was conducted to study the thermal stability of the nanocrystalline in the surface layer of Mg alloy AZ91D induced by high-energy shot peening(HESP) .Field emission scanning electron microscope(FESEM) and X-ray diffractometer were used to characterize the microstructure.Results showed that nanocrystalline produced by HESP on the surface layer of the magnesium alloy AZ91D was 60-70 nm on average.The nanocrystalline could remain stable at about 100℃,and grew up slowly between 100℃ and 200℃.When the annealing temperature reached 300℃,the growth rate of the nanocrystalline increased significantly.The kinetic coefficient n of the nanocrystalline growth was calculated to be 2-3 and the grain growth activation energy Q=39.7 kJ/mol,far less than the self-diffusion activation energy of magnesium atoms in the coarse polycrystalline material.     

超声冲击实现7A52铝合金焊接接头表面纳米化

针对7A52铝合金焊接接头表面纳米化研究尚不成熟的实际情况,利用超声冲击技术,在预设电流为2 A,超声冲击速度为1.25 min/cm2的条件下,对7A52铝合金双丝MIG焊焊接接头进行超声冲击处理,借助扫描电子显微镜及透射电子显微镜对超声冲击处理后的7A52铝合金双丝MIG焊焊接接头的表层组织进行观察、分析.发现焊接接头表层经超声冲击处理后形成塑性变形层,焊缝及热影响区的变形层厚度可达70μm左右,母材的变形层厚度可达50μm左右.同时,焊接接头表层晶粒被细化,焊缝表层的晶粒尺寸可达70~300 nm,母材的晶粒尺寸可达50~500 nm.     

Surface nanocrystallization of commercial pure titanium by shot peening

The surface nanostructures of commercial pure titanium was realized by the modified shot peening equipment commonly used in industry through the special treatment process. The results show that high-energy-shot-peening(HESP) commonly used to prepare nanostructured surface layers can be achieved by the increase of pill size, pill speed, and treatment time in the commercial shot peening equipment. XRD, SEM and TEM were used to characterize the surface layer microstructure of treated specimens. The analytic results show that the main deformation mode of commercial pure Ti is twinning. At the beginning of deformation, the dislocations are formed and twins occur within or on plane, then twins in intersection plane appear, and at last the twin characteristics disappear in the surface layer after longer treatment time. The deformation layer depth increases with treatment time in a certain period when the pill size and speed are unchanged. And in the severe plastic deformation (SPD) layer in which the twins are not identified easily by using SEM, the nanocrystalline microstructures are found under TEM. The finest grain size in the surface layer is about 40 nm, and the depth of nanostructured layers is over 60 μm. The microhardness of the nanostructured surface layers is enhanced significantly after shot peening compared with that of the initial simple.     

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。     

喷丸对23Co14Ni12Cr3Mo超高强度钢 表面性能的影响

针对23Co14Ni12Cr3Mo超高强度钢材料，研究喷丸强化对其表面性能的影响。采用扫描电镜、白光干涉仪等设备，分析喷丸强化对试样表面形貌、粗糙度、硬度、残余应力、元素含量等的影响。结果表明:喷丸强化后，试样表面留有大量弹坑，产生明显塑性变形；表面粗糙度增大，算术平均粗糙度为1.33 μm；硬度显著增大，最表层硬度由喷丸前的HV 476增加至HV 497，硬化层深度约150 μm；试样表层的残余压应力值由375 MPa增加至475 MPa，最大残余压应力值约518 MPa，位于距表面50 μm深度处，喷丸形成的残余压应力层深度约为134 μm；喷丸后试样中C、Si、Cr等各元素的质量分数均略有增加。喷丸在一定程度上改善了23Co14Ni12Cr3Mo钢材料的表面性能，有利于提高其疲劳抗力和耐腐蚀性。     

纯钛(TA2)表面纳米化及其热稳定性研究

利用超音速微粒轰击(SFPB)技术对纯钛(TA2)试样进行了表面纳米化处理,并对SFPB处理后的试样进行不同温度的热处理。通过X射线衍射(XRD)、金相显微镜(OM)、显微硬度计和透射电子显微镜(TEM)分析测试,研究纯钛表面SFPB处理后的纳米化机理及其热稳定性。结果表明:经SFPB处理后试样表层形成了尺寸约为20nm随机取向的等轴晶粒,变形机制以孪生为主,且随层深增加,形变孪晶逐渐由多系转变为单系。纳米化后在450℃热处理时,纳米晶未发生明显粗化,因而具有良好的热稳定性。     

金刚石砂轮磨削轴承用ZrO2 陶瓷表面质量研究

在氧化锆陶瓷磨削中为获得较高质量表面,采用单因素试验研究磨削深度、砂轮线速度、工件进给速度对氧化锆陶瓷精密磨削表面质量的影响规律及材料去除机理,通过超景深三维显微镜以及扫描电子显微镜,观察氧化锆陶瓷试件磨削后的表面形貌,最后用正交试验法进行优选并验证。结果表明:磨削表面的粗糙度随磨削深度、工件进给速度增大而增大,随砂轮线速度增大先减小、后增大。在磨削深度5 μm、砂轮线速度40 m/s、工件进给速度1 000 mm/min的优化组合条件下,磨削3组氧化锆陶瓷的平均表面粗糙度R_a为0.388 9 、0.417 0和0.403 7 μm。      

40 Cr 钢表面高能喷丸纳米化及其耐磨性能

为了研究40Cr钢表面纳米化对其耐磨性能的影响,对40Cr钢表面进行高能喷丸处理,获得纳米结构表层,分析了材料表面高能喷丸前后的微观组织变化,测定了纳米化材料表层的残余应力及显微硬度,研究了纳米化表层的磨损性能。结果表明:高能喷丸使40Cr钢表层发生了严重塑性变形,显微硬度较基体提高了68%,并使材料表面分布了较高幅值残余压应力,最大可达-736 MPa,残余压应力层深度达0.9 mm;高能喷丸表面纳米化能在一定程度上降低40Cr钢表面的摩擦系数,且大大减小其磨损失重,显著改善了40Cr钢的耐磨性能。     

Mechanical properties of strengthened surface layer in Ti–6Al–4V alloy induced by wet peening treatment

A modified surface layer was formed on Ti–6Al–4V alloy by wet peening treatment. The variations of the residual stress, nano-hardness and microstructure of the modified layer with depth from surface were studied using X-ray diffraction analysis, nano-indentation analysis, scanning electron microscopy and transmission electron microscopy observations. The results show that both the compressive residual stress and hardness decrease with increasing depth, and the termination depths are 160 and 80 μm, respectively. The microstructure observation indicates that within 80 μm, the compressive residual stress and the hardness are enhanced by the co-action of the grain refinement strengthening and dislocation strengthening. Within 80–160 μm, the compressive residual stress mainly derives from the dislocation strengthening. The strengthened layer in Ti–6Al–4V alloy after wet peening treatment was quantitatively analyzed by a revised equation with respect to a relation between hardness and yield strength.     

碳钢表面喷丸诱导低温B-Cr-Re共渗研究

目的进一步拓宽低温B-Cr-Re共渗技术的应用。方法采用喷丸技术对20钢表面进行预处理,处理的时间分别为0.5、1.0、1.5 h,然后进行低温B-Cr-Re固体共渗及其力学性能研究,共渗温度为600℃和650℃,保温时间6 h。利用高分辨透射电子显微镜、扫描电子显微镜、X射线衍射仪等,对预处理后基体表层结构和B-Cr-Re低温扩散层组织结构及力学性能进行表征。结果经喷丸处理后,基体表层发生严重塑性变形,晶粒发生破碎并逐渐细化,获得平均晶粒尺寸分别为50、58、65nm的纳米结构层,晶界明显增多。预处理时间越长,基体表层变形程度越严重,获得的纳米结构越明显;同时由于原子排列发生错排,阻碍了基体表层位错等缺陷的运动,故在基体表层观察到高密度位错等结构缺陷。经喷丸处理后,600℃下处理不同时间的B-Cr-Re低温共渗层组织连续、均匀,存在孔洞,平均深度约为7、8、7μm,650℃下处理不同时间的B-Cr-Re低温共渗层组织连续、均匀、致密,平均深度约为21、24、22μm,力学性能良好。结论喷丸处理后,基体表层存在较多的晶界和高密度位错,为后续B-Cr-Re的低温共渗提供了更多结构和能量支持,降低了B原子的扩散激活能,提高了B原子的扩散速度。这项工作为低温B-Cr-Re共渗技术的应用拓宽了领域。     

Synthesis and characterization ofsingle-crystalline alumina nanowires

Alumina nanowires were synthesized on large-area silicon substrate via simple thermal evaporation method of heating a mixture of aluminum and alumina powders without using any catalyst or template. The phase structure and the surface morphology of the as-grown sample were analyzed by X-ray diffractometry(XRD) and scanning electron microscopy (SEM), respectively. The chemical composition and the microstructure of the as-grown alumina nanowires were characterized using transmission electron microscope(TEM). The nanowires are usually straight and the single crystalline has average diameter of 40 nm and length of 3 - 5μm. The growth direction is along the [002] direction. Well aligned alumina nanowire arrays were observed on the surface of many large particles. The catalyst-free growth of the alumina nanowires was explained under the framework of a vapor-solid(VS) growth mechanism. This as-synthesized alumina nanowires could find potential applications in the fabrication of nanodevices.     

快速多重旋转碾压诱导Ti-6Al-4V表面纳米晶及性能研究

目的 使Ti-6Al-4V能更好地应用于海洋领域.方法 采用快速多重旋转碾压技术(FMRR)对Ti-6Al-4V表面进行冷变形处理,研究其力学性能.然后,对其进行低温等离子渗氮,渗氮温度为550℃,保温时间4 h.利用高分辨透射电子显微镜(HRTEM)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和电子显微硬度计等测试设备,对FMRR处理后的Ti-6Al-4V表层组织结构和性能以及等离子渗氮处理后表层组织结构进行表征.结果 经15、30、45 min的FMRR处理后,Ti-6Al-4V表层晶粒细化并获得了纳米结构,对应的平均晶粒尺寸为65～90、45～70和20～40 nm.此时,晶界明显增多,局部存在孪晶、小角度晶界和高密度位错等结构缺陷,电子衍射环连续.同时,Ti-6Al-4V表层结构未出现新相,晶粒细化导致衍射峰略有变宽,也提高了Ti-6Al-4V表面的显微硬度,显微硬度为325～453HV,比处理前提高了约41％.FMRR预处理的试样经过低温等离子渗氮后,基体表面的渗氮层主要包括白色化合物层和过渡层两个区域.结论 FMRR处理为后续低温渗氮提供了能量条件和结构条件,提高了渗氮的速度,最终的渗氮层厚度约为100μm.     

钛/铝异种金属冷金属过渡增材制造

采用TC4和ER2319焊丝直流/变极性冷金属过渡实现异种金属电弧增材制造，通过金相显微镜、扫描电镜、透射电镜、能谱、硬度试验、纳米压痕以及拉伸试验等方法对钛/铝构件界面组织特征与力学性能进行分析.结果表明，在钛合金表面堆积铝合金时，只有少量的钛合金熔化，钛原子扩散到液态铝合金中，形成不同长度的TiAl₃金属间化合物.10 μm左右的反应层在钛/铝界面形成.邻近钛侧的反应层均匀连续，靠近铝合金一侧的反应层呈现长条状或块状.界面反应层的显微硬度介于钛合金和铝合金显微硬度之间.构件的最高抗拉强度为111 MPa.     

PCrNi3Mo钢真空渗铬层的组织与性能

在真空条件下对PCrNi3Mo钢表面进行渗铬处理,采用X射线衍射、扫描电镜、光学显微镜、自动显微硬度仪、干滑动摩擦及电化学腐蚀等手段分析了渗铬层的组织与性能。结果表明,PCrNi3Mo钢在真空渗铬处理后表面形成了一层由Cr₂₃C₆、Cr₇C₃和(Cr,Fe)₇C₃组成的化合物渗层,渗层致密且与基体结合良好。渗层深度、硬度、耐磨性以及耐腐蚀性均随渗铬保温时间的延长而提高。对工件进行12 h保温渗铬后得到的渗铬层厚度约为11 μm,表面硬度为1117.1 HV0.5,磨擦因数最低,其磨损量为0.1225 mg,自腐蚀电流密度比基体降低了2个数量级,综合性能最优。