منابع پایان نامه درباره Technology

جذب شده تا شکست افزایش یافته است یعنی چقرمگی نمونه و کرنش موثر نمونه افزایش یافته است. علت این موضوع می تواند مربوط به رشد رسوبات Ni4Ti3 در این دما، با افزایش زمان باشد.
در دمای oC600 با افزایش زمان یک روند افزایش کاهشی در انرژی جذب شده تا شکست ملاحظه گردید. در این حالت به نظر می رسد چون دما به محدوده تشکیل رسوبات Ni3Ti2 رسیده است، افزایش زمان کسر حجمی این رسوبات را افزایش می دهد و ساختار به سمت ترد شده حرکت می کند.
با افزایش زمان عملیات حرارتی پیرسازی، سختی کاهش یافته است. علت این موضوع می تواند این باشد که با افزایش زمان، فرصت کافی برای رسوب دهی بیشتر فراهم می شود و سختی نمونه به دلیل کاهش فوق اشباعی زمینه از نیکل کاهش می یابد.
در بررسی سختی نمونه های پیر شده، اثر افزایش زمان بیشتر از اثر افزایش دما بوده است. یعنی یک حداقل زمانی لازم است تا تاثیر دما برروی سختی نمونه ها خود را نشان دهد.
پیشنهادات:
تعیین معیار مناسبی برای تعیین دما و زمان همگن سازی
اثر متغیر های فرآیند همگن سازی مانند دما، زمان و محیط سردکنندگی بر رفتار حافظه داری و خواص مکانیکی آلیاژ پیر شده
بررسی دقیق تر لزوم انجام عملیات محلولی
بررسی زمان های طولانی تر پیرسازی مانند 32 ساعت و 72 ساعت و اثر آن بر خواص مکانیکی
بررسی رفتار حافظه داری آلیاژ غنی از نیکل پیرشده در زمان های مختلف و اثر تغییر نرخ گرمایش DSC بر رفتار استحاله ای این آلیاژها
پیوست1
لیست مقالات ارائه شده:
Effect of Homogenization Time and Cooling Rate on Martensitic Transformations in Ti-57.5%wtNi Alloy, Accepted in DSL conference , Rome Italy June 2009, accepted to be published in the Special Issue of Defect and Diffusion Forum(DDF) by Trans Tech. Publications
Effect of Homogenization variables on Microstructure in Ti-57.5%wtNi Alloy, Accepted in DSL conference, Rome Italy June 2009, accepted to be published in the Special Issue of Defect and Diffusion Forum(DDF) by Trans Tech. Publications
Study on homogenization time and cooling rate on microstructure and transformation temperatures of Ni-42.5wt%Ti-3wt%Cu alloy, Accepted in DSL conference , Rome Italy June 2009, accepted to be published in the Special Issue of Defect and Diffusion Forum(DDF) by Trans Tech. Publications
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Abstract
Nitinol is well known for its thermomechanical properties and superelasticity and shape memory effect. Because of having excellent corrosion resistance, biocompatibility, the alloy has increased number of medical applications such as orthodontic wires, orthopedic devices and surgical devices. Development and growth of Nitinol applications in the industrial and commercial markets have also been fairly strong in recent years. Eyeglass frames, cellular phone antenna, high pressure sealing plug for diesel fuel injectors and over-temperature protection device for lithium ion battery are among the applications. The thermal and mechanical shape memory behavior in these alloys is dependent upon their martensitic transformation. The TiNi alloys containing more than 55 %wt nickel undergo precipitation of Ni4Ti3, Ni3Ti2, Ni3Ti phases during aging. The precipitation phase particles and the following change in the chemical composition of the matrix have a considerable effect on subsequent martensitic transformations. Each precipitation has its own range of creation time and creation temperature. That is, the aging process could be done in the way that results in desired mechanical properties and shape memory behavior. In this work, the effect time and temperature of aging on microstructure and mechanical properties of Ni-rich-NiTi alloy with Ti-57.5%wt nickel content was examined. For this aim, after melting and fabrication the ingot with desired composition, the homogenization process was examined and 1100oC and 4 hours were chose for the best results. Afterwards, by considering the result of solution treatments tests, 1100oC and 1 hour were chose for the appropriate temperature and time for solution treatments. For aging, the samples were subjected to the temperature range of 400 to 700 oC and various time periods (0.5, 1, 8, 16 hours). The optimum ultimate strength following with optimum ductility was result in aging conditions of 500oC and 16 hours. The results of hardness test show that with increasing the time of heat treatment the hardness of samples decreases. The harness of solution treated samples is higher than conventional aging treated samples.
Key words: Ni-rich NiTi alloys, Aging treatment, Mechanical properties, Martensitic transformation, Homogenization
K.N.Toosi University of Technology
Mechanical Engineering Faculty
Material Science and Engineering department
Thesis of Master of Science
Effect of aging heat treatment on microstructure and mechanical properties of Ni-rich NiTi alloy (57.5%wt. Ni)
By
Pooria Movahed
M.Sc. Advisor: Dr. Ali Shokuhfar
1Shape memory alloy (SMA)
2Shape memory effect
3Super elastic
4Pseudo elastic
5Damping
6 Shape memory alloys (SMA)
7 Chang and Read
8 Nickel Titanium Ordnance Laboratory
9 Vacuum induction melting
10 Vacuum consumable arc melting
11 Koskimaki
12 Energy Dispersive X-ray
13 Nishida and Honma
14 X-ray diffraction
15 Differential scanning calorimetry
16 Batailard
17 Stress induced martensite
18 Super elasticity
19 self-accommodating twinning
20 Detwinning
21 Upper plateau stress
22 Lower plateau stress
23 plateau
24 notch
25 Solution-treated
26 Precipitation free zone
27 Coherent
28 as-hot rolled
29 Overaging
30 Martens hardness
31 cold-drawn
32 Wire cut
33 Crosshead
34 Extensimeter
35 Sub size
36 Robertson
37

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