计算机用镁合金的组织热稳定性及力学性能

对计算机用超细晶AZ31镁合金进行了退火处理,研究了退火温度和退火时间对组织热稳定性和力学性能的影响。结果表明,随退火温度的升高,合金的晶粒尺寸逐渐增大;晶粒尺寸随保温时间的延长逐渐增大,但随退火时间的延长,晶粒长大的速率逐渐降低;超细晶AZ31合金的屈服强度和维氏硬度与晶粒尺寸之间都很好地符合Hall-Petch关系。     

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 为了研究含铜超低碳钢等温时效铜析出,对试验钢在950 ℃固溶,经650 ℃保温1、20、45 h和400~650 ℃保温1 h等温时效后,通过金相、扫描电镜和透射电镜观察及维氏硬度测试揭示等温时效对铜析出的影响规律。试验结果表明随着时效时间的增长,试验钢晶粒尺寸差别不大,但Cu时效析出颗粒的尺寸和形貌存在很大差异,反映在试验钢的平均硬度值发生变化：时效时间为1 h时,试验钢硬度值最高,平均硬度值达到189 HV;时效时间为20 h和45 h时硬度值降低,在160 HV左右。400~650 ℃保温1 h结果表明随着时效温度增长,试验钢的硬度呈现先上升后下降的趋势。     

深冷处理对TC4钛合金退火过程中微观组织和力学性能的影响

采用液氮直冷法在-196 ℃下分别对10%、20%和40%压下量的TC4双相钛合金进行12 h的深冷处理并进行500 ℃不同时间退火处理。利用光学显微镜对晶粒尺寸进行表征;利用扫描电镜(SEM)对α相和β相体积分数进行表征;利用维氏硬度仪、电子万能试验机分别对硬度和拉伸性能进行表征。通过晶粒尺寸以及α相和β相组织结构的变化,来分析材料的硬度和拉伸性能的变化原因。结果表明,随着退火时间的延长,深冷退火试样晶粒尺寸呈先下降后上升的规律,β相的体积分数逐渐减少,转变为α相。深冷12 h轧制态TC4钛合金经过1 h的退火处理后,晶粒尺寸出现小幅度的下降,这与退火过程中产生的较小晶粒有关,并且材料在轧制后继续深冷使得材料的变形能更高,在退火过程中容易产生更多的小晶粒,同时更有利于促进β相向α相转变,材料在500 ℃退火1 h时综合力学性能表现优异。当退火时间超过1 h后,材料内α相和β相两相体积分数的变化逐渐趋于平缓,并且随着退火时间的延长,晶粒粗化现象比较明显。因此,材料的强度和硬度均低于退火1 h时的强度和硬度。冷轧变形的TC4合金经12 h深冷后在500 ℃退火1 h较为理想,可获得较好的综合力学性能。     

退火对冷轧LZ91镁锂合金组织与冲压性能的影响

通过真空感应熔炼、挤压和室温轧制制备了0.9 mm厚的LZ91镁锂合金薄板,采用金相观察、维氏硬度及杯突试验研究了不同工艺退火后合金的组织及冲压性能。结果表明:冷轧LZ91合金由α相和β相组成,显微组织为纤维状,冷轧纤维呈波浪状沿轧向延伸。退火后,合金发生再结晶,α相由纤维状转变为竹节状,进一步转变为岛状,尺寸逐渐增大,β相晶粒转变为等轴状且尺寸逐渐变大;随着退火温度的升高和保温时间的延长,合金的硬度逐渐下降,杯突试验IE值逐渐增大。合金板经200℃×4 h退火后,具有较优的综合性能,此时合金IE值为7.82 mm,维氏硬度为67 HV0.025。     

球磨法制备钛纳米晶

用球磨法制备出钛纳米晶粉末.结果表明,经过24h球磨后,晶粒平均尺寸达到12—13nm粉末的氧、氮含量极低、粉末的硬度与晶粒尺寸的关系为正常的Hall-Petch关系。     

退火工艺对高纯铝重度变形组织的影响

对纯度为99.9995%的高纯铝进行了累积重度变形量为80%的冷轧变形,并对变形的高纯铝进行了不同温度和时间下的退火处理。采用微观分析以及硬度测试等手段研究了变形高纯铝退火后的组织和硬度的变化。结果表明:高纯铝经冷轧累计变形80%后硬度值达到35.9 HV0.1,比原始未变形态增加了49%,经300℃×10 min退火后高纯铝变形组织完全再结晶,得到尺寸大小为100μm的均匀细化晶粒,硬度值下降到32.0 HV0.1,比轧制态降低了11%,随保温时间的增加,出现晶粒长大的现象,硬度下降趋于平稳;当退火温度超过300℃后,随退火温度的升高和保温时间的增加,晶粒长大现象越明显,硬度下降趋势变小,趋于稳定状态。     

热处理对表面喷丸纳米晶304不锈钢力学性能的影响

利用0. 3 MPa×6 min的喷丸工艺获得表面纳米化304不锈钢,研究了退火处理对表面喷丸纳米晶304不锈钢力学行为的影响。结果表明:经0. 3 MPa×6 min喷丸处理后,表面细化层平均晶粒尺寸为36 nm,马氏体含量为50. 2%,厚度为50μm,最大(最外表面处)和最小(离表面50μm)硬度值分别为430 HV0. 5和275 HV0. 5。650℃×30 min退火处理,表面喷丸纳米晶304不锈钢晶粒尺寸为58 nm,马氏体含量显著下降为6. 4%,综合力学性能最优,最大硬度为375 HV0. 5,抗拉强度和屈服强度分别为665 MPa和320 MPa,伸长率得到较大恢复,达44%。     

磁控溅射银镀层和电镀银镀层硬度及结合性对比研究

采用电镀与中频-直流磁控溅射技术分别在Inconel 718镍基高温合金基体表面制备银镀层。使用维氏显微硬度计和微纳米划痕仪分别测量两种镀层在室温下、工况使用温度退火后、极限温度退火后的硬度与附着力;借助SEM、EDS观察测试镀层的微观形貌以及元素构成在不同保温处理后的变化。结果表明,在室温25℃下磁控溅射银镀层的显微硬度是139.7 HV,其硬度与电镀银镀层相比增强45.5%;附着力为40 N,是电镀法制得的3倍。保温处理后由于中频-直流磁控溅射法制得的银镀层的单个晶粒平均尺寸更小且分布更均匀,镀层与基体间界面的氧化被更好地抑制。相比传统电镀银镀层,400℃下磁控溅射银镀层硬度与结合性相比电镀银镀层有显著提高;但在650℃下优势较小,24 h后两种镀层都出现脱落。     

固溶处理对800H合金组织和硬度的影响

研究了不同固溶处理工艺对800H合金组织和硬度的影响。结果表明,不同固溶处理温度对800H合金晶粒尺寸有很大影响;1050～1200℃固溶处理时,晶粒正常长大,晶粒长大激活能Q=309.3 kJ/mol;1050～1100℃固溶处理后,晶内仍有大量未固溶的富铬碳化物;1150℃固溶后,晶内富铬碳化物基本溶解;在1200℃固溶处理时,随着保温时间的延长,晶粒正常长大;晶粒尺寸与硬度符合Hall-Petch关系。     

不同退火条件下AZ31镁合金的组织和硬度分析

研究了AZ31镁合金在不同的去应力退火和完全退火结合条件下组织和硬度变化.结果表明:镁合金在250～280℃退火时,晶粒先增大后减小,最终晶粒细小且均匀;但保温时间较长,退火温度为300～350℃时,晶粒尺寸比较稳定;在400℃退火处理后,短时间内晶粒立即出现异常长大现象,晶粒粗大且不均匀,合金性能较差.退火处理的最佳温度为280～350℃.退火处理温度对AZ31镁合金的硬度值有显著影响,但退火处理时间的影响却不明显.     

高纯金属钪的退火工艺

采用硬度测量和光学显微镜观察,研究了不同退火温度对锻压加工后高纯金属钪硬度和微观组织的影响。结果表明,在相同退火时间下,随着退火温度的提高,金属钪的平均晶粒度总体呈上升趋势,硬度先降低后趋于平稳。当退火温度低于725 ℃时,回复再结晶过程相对缓慢,平均晶粒度增长有限,而硬度随退火温度的升高持续降低,在725 ℃时达到最低点;高于725 ℃时,退火温度越高平均晶粒度越大,硬度已经趋于稳定不随退火温度的升高而变化。故高纯金属钪最佳退火工艺为725 ℃×30 min。经725 ℃×30 min退火后,锻压加工后的高纯金属钪达到完全退火态,晶粒均匀,平均晶粒尺寸为135 μm,硬度值由退火前的169.5 HV2下降至退火后的129.6 HV2。     

Microhardness measurements and the Hall-Petch relationship in an AlMg alloy with submicrometer grain size

An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (∼90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements.     

Microhardness measurements and the Hall-Petch relationship in an Al---Mg alloy with submicrometer grain size

An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements.     

大应变切削制备的超细晶纯铜切屑热稳定性的研究

采用不同前角的刀具对纯铜进行大应变切削加工,对获得的超细晶纯铜切屑进行不同温度的退火处理.利用扫描电子显微镜(SEM)和维氏硬度测量仪进行检测,分析不同前角和退火温度对超细晶纯铜切屑微观组织和力学性能的影响.结果表明:用0°前角刀具进行大应变切削加工后,切屑晶粒平均尺寸为0.3μm、硬度为160HV,在200～280℃...     

An investigation of thermal stability and microhardness of electrodeposited nanocrystalline nickel-21% iron alloys

The thermal stability of an electrodeposited nickel-21% iron alloy with an average grain size of approximately 14 nm was investigated. Samples were annealed for 90 mins in the temperature range of 373–773 K. The results of this study showed that grain growth started after annealing at and above 400 K. Two regimes of grain growth were identified. It is suggested that the low temperature regime (below 575 K) is accommodated mainly by the grain boundary diffusion, while the high temperature regime is assisted by the lattice diffusion. The microhardness results also confirm the presence of these two regimes. The position of the (111) XRD peaks indicated a sudden decrease in the lattice parameter after annealing at 773 K, which is attributed to the loss of connectivity of the nanosize grains. The variation of hardness with grain size followed the Hall-Petch relationship.     

TB2钛合金等通道转角挤压变形过程的应变分析及实验研究

运用有限元方法对TB2钛合金等温等通道转角挤压过程进行有限元模拟及实验研究。模拟结果表明,材料变形结束后的等效应变分布规律为自下而上应变逐渐减小,平均应变分别为1.46,1.18,1.07。实验结果发现,微观组织得到了明显细化,平均晶粒尺寸为30μm。采用测量显微硬度的方法衡量变形均匀性发现,硬度分布规律与有限元模拟应变分布规律一致,3个部位的平均硬度分别为399.1,396.6,390.5,均大于原始材料的硬度302.4。     

退火工艺对变形高纯Yb微观组织的影响

对纯度为99.99%的高纯Yb进行总变形量为35.6%的多道次室温轧制变形加工,并对其分别在240、270、300、330、360 ℃进行退火处理,研究了退火工艺对变形高纯Yb显微组织和显微硬度的影响。结果表明,最佳退火工艺为270 ℃×0.5 h,经270 ℃×0.5 h退火后,变形高纯Yb完全再结晶,晶粒细小、均匀,平均晶粒度为22.5 μm左右,硬度值下降至18.96 HV0.5。随着退火温度的升高,试样的平均晶粒尺寸呈上升趋势,显微硬度呈降低趋势并趋于平稳。     

热处理对快速凝固ZK60镁合金薄带组织和硬度的影响

采用单辊甩带法制备了ZK60镁合金薄带,研究了不同条件热处理薄带的组织和显微硬度。结果表明,薄带由晶粒尺寸8μm的等轴α-Mg、球状β′2相和少量杆状β′1相组成;热处理温度300℃时,晶粒无长大;温度300℃时,晶粒显著长大。原始薄带显微硬度约为50HV,300℃×2h热处理后显微硬度值最大约为80HV;β′1和β′2相的弥散强化作用是薄带硬度提高的内在原因。     

Hardness of porous nanocrystalline Co-Ni electrodeposits

The Hall-Petch relationship can fail when the grain size is below a critical value of tens of nanometres. This occurs particularly for coatings having porous surfaces. In this study, electrodeposited nanostructured Co-Ni coatings from four different nickel electroplating baths having grain sizes in the range of 11–23 nm have been investigated. The finest grain size, approximately 11 nm, was obtained from a coating developed from the nickel sulphate bath. The Co-Ni coatings have a mixed face centred cubic and hexagonal close-packed structures with varying surface morphologies and different porosities. A cluster-pore mixture model has been proposed by considering no contribution from pores to the hardness. As the porosity effect was taken into consideration, the calculated pore-free hardness is in agreement with the ordinary Hall-Petch relationship even when the grain size is reduced to 11 nm for the Co-Ni coatings with 77±2 at% cobalt. The present model was applied to other porous nanocrystalline coatings, and the Hall-Petch relationship was maintained.