Mechanical Behavior of Commercially Pure Titanium Weldments at Lower Temperatures
- PDF / 6,590,670 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 72 Downloads / 211 Views
JMEPEG https://doi.org/10.1007/s11665-018-3307-9
Mechanical Behavior of Commercially Pure Titanium Weldments at Lower Temperatures R.K. Gupta, V. Anil Kumar, and X. Roshan Xavier (Submitted September 6, 2017; in revised form December 2, 2017) Commercially pure titanium is used for low-temperature applications due to good toughness attributed to single-phase microstructure (a). Electron beam welding (EBW) and gas tungsten arc welding (GTAW) processes have been used for welding two grades of commercially pure titanium (Grade 2 and Grade 4). Martensitic microstructure is found to be finer in the case of EBW joint as compared to GTAW joint due to faster rate of cooling in the former process. Weldments have been characterized to study the mechanical behavior at ambient (298 K) and cryogenic temperatures (20 and 77 K). Strength of weldments increases with the decrease in temperature, which is found to be more prominent in case of Grade 4 titanium as compared to Grade 2. Weld efficiency of Grade 4 is found to be higher at all the temperatures (ambient, 77 and 20 K). However, ultimate tensile strength/yield strength ratio is higher for Grade 2 as compared to Grade 4. % Elongation is found to increase/retained at cryogenic temperatures for Grade 2, and it is found to decrease for Grade 4. Electron backscattered diffraction analysis and transmission electron microscopy of deformed samples confirmed the presence of extensive twinning in Grade 2 and the presence of finer martensitic structure in Grade 4. Fractography analysis of tested specimens revealed the presence of cleavage facets in Grade 4 and dimples in specimens of Grade 2. Higher strength in Grade 4 is attributed to higher oxygen restricting the twin-assisted slip, which is otherwise prominent in Grade 2 titanium. Keywords
CP titanium, cryogenic properties, EBW, GTAW
1. Introduction Unalloyed titanium and its alloys are preferred materials for aerospace, chemical and power sectors due to their superior toughness at ambient and cryogenic temperatures and corrosion resistance in aggressive environments (Ref 1-4). Titanium is widely used as dental implants because of its suitable mechanical properties coupled with excellent bio-compatibility (Ref 5, 6). Commercially pure (CP) grade Ti is also used for low temperature applications due to its single-phase structure which does not undergo any phase transformation with temperature and can maintain the required level of ductility at cryogenic temperatures. The alloying elements in titanium stabilize either a phase or the b phase. In CP titanium, oxygen is an interstitial element and an effective a stabilizer, which improves the strength of pure titanium and is considered as alloying elements also. Iron is a b stabilizer and a eutectoid former which is present as an impurity and forms intermetallic compound. However, the sluggishness of intermetallic formation and the eutectoid reaction results in retention of metastable b (Ref 2, 7). Many of the pressure vessels are made through hot forming/superplastic forming/spinning follo
Data Loading...
