Radiographic inspection of porosity in Ti-6Al-4V laser-welded joints

Abstract

Widely used in dentistry, Ti-6Al-4V alloy is difficult to cast and solder, as it frequently exhibits pores inside the structure. This study was conducted to evaluate the effect of joint openings and diameters of laser-welded joints executed in Ti-6Al-4V structures on the presence of pores as checked by radiographic procedures. Sixty dumbbell rods with central diameters of 1.5, 2.0 and 3.5 mm were created from Ti-6Al-4V-wrought bars. Specimens were sectioned and welded using two joint openings (0.0 and 0.6 mm). The combination of variables created six groups (n = 10). Laser welding was executed using 360V/8ms (1.5 and 2.0 mm) and 380V/9ms (3.5 mm), with the focus and frequency set to zero. The joints were finished, polished and submitted to radiographic examination. The radiographs were visually examined for the presence of pores in the joints, qualitatively. The percentage of radiographic presence of pores was calculated without counting pores per joint. Data were analyzed using a chi-square test (α = 0.05). For the 1.5-mm specimens, the incidence of pore presence was significantly higher (p = 0.0001) when using 0.6-mm joint openings (40%) compared to 0.0-mm openings (0%). For the 2.0-mm specimens, there was no significant difference between groups (p = 0.2008). However, for the 3.5-mm specimens, the incidence of pore presence was lower (p = 0.0061) for 0.6-mm openings (50%) compared to 0.0-mm openings (70%). Therefore, laser welding of Ti6Al-4V structures with thin diameters provides the best condition for the juxtaposition of the parts.

Effect of joint design and welding type on the flexural strength and weld penetration of Ti-6Al-4V alloy bars

“…Although laser welding has obtained satisfactory results in terms of welded area, this fact was not related to higher mechanical joint strength, possibly due to the increased incidence of pores and to the lower ductility of the welded joint, as observed in the SEM analysis. 21,26 A significant (P<.001), but moderate (0.55), correlation was found between the flexural strength values and the weld penetration area for both welding methods. This finding is in accordance with previous investigations and indicates that the weld penetration ability is important in determining the final resistance of the welded framework.…”

“…Additionally, a dye-revealing liquid (VP 30; Metal-Chek) was applied to detect any surface failure. 22,26,32 Specimens that showed failures were discarded and replaced.…”

“…13,21 Although studies have demonstrated that the welding of dental frameworks can correct dimensional errors, some limitations should be considered, including the formation of pores, cracks, and internal voids due to incomplete welding penetration. 19,[22][23][24][25][26][27] These defects can act as stress concentrators, which can lead to premature failures of the titanium infrastructures. 27 The welding penetration is the main factor affecting framework strength, and different joint designs have been proposed to improve its performance.…”

Evaluation of X-shaped welded joints with Co-Cr alloy under different welding parameters: analysis by micro-CT and flexural strength

“…The studies focused on prosthetic frameworks were developed to optimize their production by the use of prefabricated bars and welding techniques other than conventional welding (Lyra e Silva, et al 2012;Silveira-Júnior, et al 2012;Castro, et al 2015;Simamoto-Júnior, et al, 2015). Studies have been conducted to evaluate the types of welding techniques (Wang & Welsch, 1995;Baba & Watanabe, 2005;Rocha, et al 2006;Zupancic, et al 2006;Barbi, et al 2012;Lyra e Silva, et al 2012;Nuñez-Pantoja, et al 2012;Atoui, et al 2013;Castro, et al 2013;Castro, et al 2015;Matos, et al 2015;, the settings of welding equipment (Chai & Chou, 1998;Baba & Watanabe, 2005;Akman, et al 2009; Lyra e Silva, et al 2015), the types of alloys used (Rocha, et al 2006;Watanabe & Topham, 2006;Takayama, et al 2012;Takayama, et al 2013;Lyra e Silva, et al 2015;Matos, et al 2015), the settings of the joints (Zupancic, et al 2006;Nuñez-Pantoja, et al 2012;Takayama, et al 2012;Kokolis, et al 2015;Simamoto-Júnior, et al 2015), and mechanical methods of evaluation of these weld joints (Nuñez-Pantoja, et al 2011;Takayama, et al 2012;Takayama, et al 2013;Castro, et al 2015).…”

“…Among the welding techniques, two have been identified for dental use: laser welding (Berg, et al 1995;Wang and Welsch, 1995;Chai & Chou, 1998;Baba & Watanabe, 2005;Akman, et al 2009;Byrne, 2011;Nuñez-Pantoja, et al 2011;Barbi, et al 2012;Nuñez-Pantoja, et al 2012;Silveira-Júnior, et al 2012;Takayma, et al 2012;Atoui, et al 2013;Castro, et al 2013;Takayama, et al 2013;Castro, et al 2015;Kokolis, et al 2015;Matos, et al 2015) and TIG or plasma welding (Wang & Welsch, 1995;Taylor, et al 1998;Rocha, et al 2006;Byrne, 2011;Barbi, et al 2012;Lyra e Silva, et al 2012;Nuñez-Pantoja, et al 2012;Silveira-Júnior, et al 2012;Atoui, et al 2013;Castro, et al 2013;Castro, et al 2015;Matos, et al 2015;Simamoto-Júnior, et al 2015). Both have some advantages: welding can be performed directly on the model (Chai & Chou, 1998;Baba & Watanabe, 2005;Rocha, et al 2006;Zupancic, et al 2006;Barbi, et al 2012;Silveira-Júnior, et al 2012;Castro, et al 2015), energy can be concentrated in a small area (Rocha, et al 2006;Barbi, et al 2012;Lyra e Silva, et al 2012;…”