بررسی رفتار تغییرشکل گرم و خواص حافظه‌داری آلیاژ حافظه‌دار دمای بالا Ni50Ti40Hf10

نوع مقاله : مقاله پژوهشی

نویسنده

استادیار، دانشکده عمران و منابع زمین، دانشگاه آزاد اسلامی واحد تهران مرکزی، تهران، ایران

چکیده

آلیاژهای حافظه‌­دار NiTiHf برای کاربردهای صنعتی در دمای بالا بدلیل دمای استحاله بالا و پایداری حرارتی و قیمت پایین­‌تر، بسیار مورد توجه می‌­باشد. البته خواص حافظه‌­داری آنها از آلیاژهای دوتایی NiTi کمتر می‌­باشد. راه حل این مشکل افزایش استحکام آلیاژ جهت جلوگیری از وقوع تغییرشکل پلاستیکی ناشی از لغزش می‌­باشد. یکی از راه‌های بهبود خواص حافظه‌­داری انجام عملیات ترمومکانیکی می‌­باشد. در این پژوهش آلیاژ Ni50Ti40Hf10 در کوره قوس تحت خلاء آلیاژسازی و ریخته گری شد. سپس آزمون کشش گرم بر روی نمونه­‌ها با نرخ کرنش s-1 01/0 در دماهای 800، 900، 1000 و 1100 درجه سانتی‌گراد انجام شد. همچنین نمونه‌­ها در دمای 1000 درجه سانتی‌گراد با کاهش ضخامت‌­های 10، 15، 20 و 30 درصد نورد گرم شدند. جهت بررسی خواص حافظه‌­داری و تعیین میزان کرنش بازیابی و نسبت بازیابی با استفاده از آزمون خمش کرنش‌های اعمالی 6/2 تا 6 به روی نمونه­‌ها اعمال شد. نتایج آزمون کشش گرم نشان داد که دمای 1000 درجه سانتی‌گراد به دلیل مناسب بودن میزان شکل‌­پذیری آلیاژ برای انجام نورد گرم قابل قبول می‌­باشد. حداکثر کرنش بازیابی در نمونه ریختگی 7/5 با نسبت بازیابی 88 درصد بود. با اعمال 10 درصد نورد گرم، میزان کرنش بازیابی و نسبت بازیابی به 8/5 و 92 افزایش یافت و در ادامه با اعمال 20 درصد نورد این مقادیر به 9/5 و 94 افزایش یافت. تشکیل دانه­‌های یکنواخت و هم محور در ریزساختار نمونه­‌ها حاکی از وقوع تبلور مجدد دینامیکی می­‌باشد که منجر به افزایش میزان کرنش بازیابی گردید.

کلیدواژه‌ها

عنوان مقاله [English]

Investigating Hot Deformation Behavior and Shape Memory Properties of Ni50Ti40Hf10 High Temperature Shape Memory Alloy

نویسنده [English]

  • Majid Belbasi
Department of Civil and Earth resources, Central Tehran Branch, Islamic Azad University, Tehran, Iran
چکیده [English]

NiTiHf high temperature shape memory alloys are highly popular for high temperature industrial applications due to their high transformation temperature, thermal stability and lower cost. However, they have weaker shape memory properties than NiTi binary alloys. The solution to this problem is to increase the strength of the alloy in order to prevent plastic deformation caused by slipping. Thermomechanical treatment is a method to improve the recovery strain. In this research, the Ni50Ti40Hf10 shape memory alloy was cast by vacuum arc melting and then the hot tensile test was performed on the samples with a strain rate of 0.01 s-1 at 800, 900, 1000 and 1100 °C, also specimens were hot- rolled at 1000 °C with a reduction of thicknesses by 10, 15, 20 and 30%.  To determine the amount of recovery strain and recovery ratio by bending test strains of 2.6 to 6 were applied to the samples. The results of the hot tensile test showed that the temperature of 1000 °C is acceptable for hot rolling due to the suitable ductility of the alloy. The maximum recovery strain in the cast sample was 5.7 with a recovery ratio of 88%. By applying 10% of hot rolling, the recovery strain and recovery ratio increased to 5.8 and 92 respectively, while after 20% of rolling, these values increased to 5.9 and 94. The formation of uniform and coaxial grains in the microstructure of the samples indicated the occurrence of dynamic recrystallization, which led to an increase in the recovery strain.

کلیدواژه‌ها [English]

  • NiTiHf shape memory alloys
  • Hot rolling
  • Hot tensile
  • Recovery strain
  • Recovery ratio

مراجع

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مهندسی ساخت و تولید ایران
دوره 9، شماره 6
شهریور 1401
صفحه 49-58

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