processing map
در نشریات گروه مواد و متالورژی-
مقدمه و اهداف
تعیین معادلات ساختاری توصیف کننده تنش سیلان مواد، بررسی ریزساختار و تهیه نقشه فرایندی، جهت طراحی و بهینه سازی در شکل دهی فلزات ضروری است. هدف در این مقاله، دست یابی به یک رابطه میان تنش، کرنش، دما و نرخ کرنش برای آلیاژ Al-7.5Mg جهت استفاده از آن در فرایند شکل دهی می باشد.
مواد و روش هادر این پژوهش، از نمودار های تنش- کرنش در چهار دما و سه نرخ کرنش و حذف اصطکاک با روش های تجربی و محاسباتی، استفاده شد. مقدار انرژی فعال سازی تغییر شکل داغ در مدل آرنیوسی محاسبه گردید. نقشه فرایندی جهت برقراری ارتباط میان تنش، دما و نرخ کرنش، در کرنش 0/6 ترسیم و منطقه ناپایداری در دما و نرخ کرنش مشخص، تعیین شد. جهت مطالعه ریزساختار آلیاژ نیز از عملیات متالوگرافی استفاده گردید.
یافته هابا افزایش میزان کرنش، مقدار انرژی فعال سازی تغییر شکل داغ در مدل آرنیوسی افزایش یافت. همچنین، کاهش دما و افزایش نرخ کرنش منجر به صعودی شدن پارامتر زنر- هولمن گردید. نقشه فرایندی ترسیم شده نشان داد که با افزایش دما و کاهش نرخ کرنش، منطقه ناپایداری گسترش می یابد. نتایج آزمون متالوگرافی نشان داد که به دلیل محتوای بالای منیزیم در این آلیاژ، تبلور مجدد دینامیکی در آن رخ داده است.
نتیجه گیریدر این تحقیق، مدل آرنیوسی (به عنوان یک مدل پدیدار شناختی) با استفاده از آزمون فشار کرنش صفحه ای داغ بر روی ورق اکسترودی آلیاژ Al-7.5Mg به درستی استخراج گردید و رابطه میان تنش، دما، کرنش و نرخ کرنش به کمک معادلات ساختاری و مدل آرنیوسی حاصل شد.
کلید واژگان: معادلات ساختاری، نقشه فرایندی، آلیاژ Al-7.5Mg، آزمون فشار کرنش صفحه ای داغ، ریزساختارIntroduction and ObjectivesDetermining the constitutive equations which describe the material flow stress, microstructural investigation, and preparing a processing map are essential for designing and optimizing metals forming. The aim of this paper is to obtain a relationship between stress, strain, temperature, and strain rate for Al-7.5Mg alloy in order to use it in the forming process.
Materials and MethodsIn this study, stress-strain diagrams at four temperatures and three strain rates and friction elimination using experimental and computational methods were used. The activation energy value of hot deformation was calculated in the Arrhenius model. A processing map at strain 0.6 was drawn to establish the relationship between stress, temperature, and strain rate, and the instability region at a specific temperature and strain rate was determined. The metallography examination was performed to study the microstructure of the alloy.
ResultsIn the Arrhenius model, the activation energy value of hot deformation increased with increasing strain. As the temperature decreased and the strain rate increased, the Zener-Hollomon parameter also increased. The instability region increased with increasing temperature and decreasing strain rate. The metallography test results showed that dynamic recrystallization occurred due to the high magnesium content in this alloy.
ConclusionIn this paper, the Arrhenius model (as a phenomenological model) was correctly extracted using a hot plane strain test on an extruded plate of Al-7.5Mg alloy, and a relationship between stress, temperature, strain, and strain rate was obtained using the constitutive equations and the Arrhenius model.
Keywords: Constitutive Equation, Processing Map, Al-7.5Mg, Hot Plane Strain Compression Test, Microstructure -
The efficiency parameter, which is frequently utilized in the literature, can be expressed as η=(2m/m+1), where m is the strain rate sensitivity. The efficiency parameter is determined from a set of m values based on the strain rate and the temperature displayed in a three-dimensional map known as the power dissipation map. This method works if the test results for σ vs. 𝜀̇ at constant strain and temperature have a power-law distribution. Otherwise, it is incorrect to assess dissipation efficiency using the of the 𝑙𝑛𝜎 − 𝑙𝑛𝜀̇ graph. The present study proposes additional adjustments to the existing ones suggested in the literature for the prior technique by offering a scheme for evaluating η. Power dissipation maps for different techniques are developed at strains of 0.2 and 0.7 using X80 steel as a model material. In spite of the fact that the approaches rely on different assumptions and that there are differences in the temperature and strain rate at which the dissipation efficiency peak appears, there are some similarities in the power dissipation maps of all approaches when they are compared at different strains. In conclusion, although the conventional approach is erroneous, it is the most feasible and straightforward one.Keywords: Metal Forming, Hot Deformation, Efficiency Parameter, Dissipation Map, Processing Map
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Semi-stable β-titanium (Ti-3873) Ti-3Al-8Mo-7V-3Cr alloy with excellent workability properties has been designed based on high demanded aircraft Ti-5Al-5Mo-5V-3Cr alloy according to semi-experimental d-electron approach. The aim of the present research is to investigate the deformation behavior of Ti-3873 alloy via warm compression test. For this purpose, compression test has been conducted in the temperature range of 650-850 °C and strain rates of 0.001,0.1 and 1, 1 s-1 at dual phase α/β and single phase β regions. The test was continued up to plastic strain of 0.7. For establishing the relationship between the microstructure and flow behavior, the initial and subsequent microstructure of the specimens after warm deformation was studied via optical and scanning electron microscopes. The microstructural evaluation and flow curves revealed that dynamic recovery and partial continuous dynamic recrystallization were the dominant restoration mechanisms. The results showed that softening has been increased in the temperature range of 800-850 °C and strain of 0.001 and 0.1 s-1 which is confirmed by the activation energy calculated from the sinus hyperbolic equation. The activation energy for dual phase α/β and single phase β regions are determines as 429 kJ/mol and 353 kJ/mol, respectively. The higher value of activation energy for α/β dual phase region is attributed to dynamic globularization of α lamellas. The preferable regions for hot workability of the alloy were achieved at the temperature range of 800-850 °C and strain rate of 0.01-0.001 s-1 corresponding to the peak efficiency of 39% in the processing map.
Keywords: Ti-3Al-8Mo-7V-3Cr Alloy, Recovery, Recrystallization, Activation Energy, Processing Map -
در این پژوهش، به بررسی رفتار تغییر شکل گرم فولاد ابزار گرم کار W360، با انجام آزمایش فشار گرم در محدوده دمایی 1000 تا 1200 درجه سانتی گراد و نرخ های کرنش 0/001، 0/01، 0/1 و 1 بر ثانیه پرداخته شده است. مطابق نتایج حاصل، تبلور مجدد دینامیکی مهم ترین عامل ترمیم این آلیاژ حین تغییر شکل گرم است. در فولاد W360 با افزایش دما و افزایش نرخ کرنش، تبلور مجدد افزایش یافته است. در دمای 1000 درجه سانتی گراد و نرخ کرنش یک بر ثانیه ساختار کاملا تبلور مجدد یافته حاصل شده است و در دمای 1200 درجه سانتی گراد وقوع رشد دانه کاملا مشهود است. همچنین با رسم نقشه فرایند این فولاد، محدوده بهینه تغییر شکل گرم آن تعیین شد. تصاویر ریزساختاری حاصل از آزمایش فشار گرم نشان داد که در دمای 1000 درجه سانتی گراد و نرخ کرنش 0/01 بر ثانیه، تبلور مجدد آغاز شده و با افزایش دما و افزایش نرخ کرنش، به دلیل افزایش انرژی ذخیره شده و درنتیجه افزایش مکان های مساعد برای جوانه زنی، تبلور مجدد توسعه می یابد. نتایج حاصل از رسم نقشه فرایند نشان داد، منطقه مناسب تغییر شکل گرم فولاد مورد بررسی، محدوده دمایی 1050 تا 1150 درجه سانتی گراد و نرخ کرنش 0/1 تا 1 بر ثانیه است.
کلید واژگان: فولاد ابزار گرم کار W360، آزمایش فشار گرم، تبلور مجدد دینامیکی، نقشه فرایندIn this research, the hot deformation behavior of W360 tool steel was investigated using hot compression test at 1000-1200°C and strain rates of 0.001, 0.01, 0.1, and 1 s-1. According to the results, dynamic recrystallization was found the most important restoration factor of this alloy during hot deformation. Recrystallization was enhanced with an increase in temperature and strain rate. Also, the hot working process was optimized by drawing the processing map of this steel. Microstructural images obtained from the hot compression test showed that recrystallization started at 1000°C and the strain rate of 0.01 s-1 and developed with increasing temperature and strain rate due to an increase in the stored energy and suitable regions for nucleation. The results of drawing the processing map showed that the best hot deformation region was the temperature range of 1050-1150°C and strain rates of 0.1-1 s-1.
Keywords: W360 hot work tool steel, Hot compression test, Dynamic recrystallization, Processing map -
Hot workability of as-extruded high Gd content Mg-5Gd-0,5Zn-0.5Zr-2.5Nd alloy was investigated using the hot compression test in a temperature range of 300-500 °C and strain rates of 0.001-1s-1. Hot workability assessment was conducted by capturing microstructural evolution of high temperature deformed samples, and by constructing power dissipation and instability maps. Using experimental data of hot compression tests, the power dissipation map of the alloy was constructed, in which a domain of dynamic recrystallization (DRX) occurred at the temperature range of 350-450 °C and strain rate of 0.001-0.1 s-1, representing the optimum hot working window. Furthermore, the processing map of the alloy was constructed, and flow instability regions were also indicated based on the Ziegler's flow instability criterion.
Keywords: Magnesium alloy, Rare earth metals, Processing map, Hot workability -
International Journal of iron and steel society of Iran, Volume:15 Issue: 2, Summer and Autumn 2018, PP 54 -61In this study, the hot deformation processing map of AISI 304 austenitic stainless steel in two initial grain sizes of 15 and 40 μm was investigated. For this purpose, cylindrical samples were used in the hot compression test at the temperature range of 950-1100 °C and the strain rate of 0.005-0.5% s-1. At first, the relationship between the peak stress and Zener-Hollomon parameter was obtained and their microstructures were studied, then the strain rate sensitivity and the processing map were determined at the strains of 0.5 and 0.7. It was found that in the aforementioned temperature range and strain rate ,the prevailing softening mechanism was the dynamic recrystallization process. Instability regions were observed at lower temperatures and higher strain rates, associated with the occurrence of necklace phenomenon in both grain sizes, as well as the semi-necklace structure in coarse-grained steel and in fine grain steel to the formation of geometrically necessary dislocation along the grain boundaries. Moreover, it was associated with the development of cell structure interior the grains. In addition, with an increase in temperature and a decrease in strain rate, both the power dissipation efficiency and the strain rate sensitivity increased, indicating an increase in the volume of the recrystallized materials in a constant strain and a decrease in the localization of the plastic flow.Keywords: Austenitic stainless steel, Dynamic recrystallization, Processing map, Grain size effect
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In the present study, the microstructural changes of a Nickel based superalloy Nimonic
80A during a non-isothermal deformation were studied. Therefore, microstructure evolution during hot side pressing test was predicted with combined methods of finite element analysis and processing map of the material. The predicted results were validated through experimental microstructural studies. The results show that the distribution of deformation parameters (i.e. strain, strain rate, and temperature) is non-uniform in the deformed samples. The severity of this non-uniformity depends on the amount of sample reduction. High reduction value at one step forging can cause flow localization and non-uniform dynamic recrystallization, which results the formation of adiabatic shear bands, while using the lower reduction value at each forging step, leads to more uniformly distribution of the deformation parameters and thus uniform the dynamic recrystallization with the stable flow. Hence the workability and microstructure of the Nimonic 80A alloy are mainly depends on the deformation path.Keywords: Hot deformation, Nimonic 80A, Processing map, Microstructure, finite element analysis
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