تقصي تأثير عمليات اللحام بالليزر ومتغيراتها على لحامات سبيكة التيتانيوم
Investigation the Effect of Laser Welding Processes and their Parameters on Titanium Alloy Welds
- الباحث
- مروة محمد عبد الرضا
- المشرف
- عبد السميع جواد عبد الزهرة الجلبي
- الجامعة
- جامعة بابل
- الكلية / القسم
- هندسة المواد / هندسة المعادن
- الشهادة
- دكتوراه
- السنة
- 2023
- لغة الرسالة
- E
- الكلمات المفتاحية
- اللحام بالليزر;سبائك التيتانيوم;متغيرات اللحام;هندسة المعادن
Abstract
Titanium (Ti) alloys are engineering materials widely used in various fields including aviation, marine, petrochemical, sports, medical and more. During manufacturing, all of these applications require the use of welding processes. Laser welding is one of the most important processes used to weld Ti alloys, because Ti has a high reactivity with atmospheric components at high temperatures. This leads to the formation of hard and brittle compounds that promote the development of weld defects. Therefore, it requires the use of inert gas shielded welding processes. The research objectives are to study the effect of changing laser welding methods and welding parameters on Ti alloy welds. It is study the effect of these parameters on weld geometry (weld penetration depth and weld zone width), HAZ width, microstructure, hardness, tensile strength and fracture surfaces. In this work, continuous fiber and pulsed Nd:YAG lasers were used for welding similar 3mm thick butt joints of CP-Ti and Ti-6Al-4V alloys. Two variables were selected for each welding method: laser power and welding speed with four values for each variable. Several tests have been carried out to evaluate the performance of laser welds, including non-destructive tests (energy dispersive spectrometry, X-ray diffraction, X-ray radiography and macrography to measure the HAZ width). Other tests such as optical and scanning electron microscopy, microhardness, tensile test and fractography were also performed. The most important results showed that the HAZ width in fiber laser welds decreased with increasing welding speed. The HAZ’s of the Ti-6Al-4V alloy welds were wider than those that appeared in the CP-Ti welds. The maximum penetration depths of the Nd:YAG CP-Ti and Ti-6Al-4V welds, joined from both sides, were slightly higher than those of the one side fiber welds. The fusion zone (FZ) microstructure of the CP-Ti laser welds consisted of acicular α, and there was no martensite formed. However, the FZ structure of the Ti-6Al-4V welds showed an acicular α⸜ (martensite) phase. The HAZ microstructure of the CP-Ti welds was mainly composed of acicular α near the FZ, which gradually decreased while moving towards the BM. On the other hand, the HAZ microstructure of the Ti-6Al-4V welds consisted of a small amount of acicular α⸜, primary α and β grains near the BM, and a large amount of acicular α⸜ near the FZ. The maximum hardness values across the welds were in the weld center, and decreased steeply while advancing towards the BM. The hardness across the Nd:YAG laser welds was higher than that across the fiber welds, and was significantly higher across the Ti-6Al-4V welds than that across the CP-Ti welds. The maximum hardness across the welds was generally associated with the lowest heat input. For the CP-Ti welds joined by the fiber and Nd:YAG laser methods, the maximum tensile strength values were 790MPa and 850MPa respectively, while for the Ti-6Al-4V alloy welds were 1639MPa and 1695MPa respectively. The most noticeable defects observed in laser welds were the incomplete penetration and a few of porosity mainly related to the lowest heat input, in addition to deep craters associated with the highest heat input. There were no indications of cracks across all laser welds. Finally, the fracture behavior of all laser welds was brittle, except the welds that showed the highest tensile strengths, where the fracture mode was a brittle- ductile.
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