WE Seminar: Jianxiong Li and Boeing Smith

Effect of high-temperature exposure on Ti/SS and Ti/Nb/SS impact spot welds

Jianxiong Li

Advised by Dr. Glenn Daehn

Abstract

Titanium alloy (Ti alloy) and stainless steel (SS) can be joined successfully by vaporizing foil actuator welding. A niobium (Nb) interlayer can be introduced to obtain reliable joints in one blow. Both types of bonds give base metal failure during lap shear tests in as-welded condition. The effect of the Nb interlayer on the stability against high-temperature exposure (HTE) was studied. The Nb interlayer can prevent the interdiffusion between Ti and SS and thus minimize the deterioration of Ti-Nb-SS impact spot welds when the exposure temperatures are lower than 800 °C. For Ti-Nb-SS welds, no obvious change of interfacial microstructure was found from 300 to 600 °C, which is different from Ti-SS welds containing a continuous intermetallic compound (IMC) layer at 700 °C. When the exposure temperature is equal to or larger than 800 °C, the lap shear strengths of Ti-Nb-SS impact spot welds decrease significantly due to the formation of a continuous IMC layer between Nb and SS, and the failure modes change from base metal failure to interfacial fracture. For Ti-SS welds, the lap shear strengths decrease slightly from 300 to 600 °C while significantly from 700 to 950 °C due to phase transformation, IMC and reheat crack formation. The acceptable operation temperature ranges for Ti-SS and Ti-Nb-SS spot impact welds under HTE are suggested.

Bio

I received my undergraduate and master both from Tianjin University in China, both focusing on materials processing technologies. I came to USA for PhD in 2017. I am focusing on dissimilar metal welding using vaporizing foil actuator welding. The material combinations I have worked with include Ti/stainless steel, Al/Steel, NiTi/Stainless steel, and NiTi wires. I also worked on axisymmetric shearing, forming and welding of tubes using vaporizing foil actuators. Heat treatment of dissimilar welds is another field I was working on. I familiarized myself with microscopic techniques such as OM, SEM (EDS) and EBSD. After work, I prefer hiking, swimming and playing mahjong (tile-based game) with friends. Watching comedy, news, and historical programs are also my favorite time killers.

OES, IIT, HV Maps, and CVN Instrument Capabilities and Applications

Boeing Smith

Advised by Dr. Antonio Ramirez

Abstract

Boeing’s main research looks to find a quantitative correlation between Fundamental Indentation Techniques and Impact Toughness. However, during this work OSU WE has obtained and used different instruments (OES Spectrometer, Instrumented Macro-Indenter, Microhardness Mapper, and the Charpy V-Notch Hammer) to obtain our hardness and toughness measurements most of which is new and unfamiliar to the OSU Welding Engineering Department. This talk looks to go over this new equipment and its capabilities. The OES spectrometer has a new small sample adapter that can be used for samples less than half an inch. The Frontics AIS 3000 donated by Shell has the capabilities to measure fracture toughness, residual stress, and tensile properties; however, some of these techniques have some skepticism in the industry. The Microhardness Mapper has some capabilities that have not been utilized as much as they could be including the loop and fill methods along with LECO hardness verification blocks that can be used as needed with permission. The new CVN should be installed and should be available for use January, 1 2020; however, there are some very important safety and methodology concerns to take when using the new equipment which will be addressed.

Bio

Boeing Smith grew up in southeastern Ohio and is from a little town called Gallipolis right across the river from Point Pleasant, West Virginia. Due to such when Dr. Benatar talks about the Silver Bridge collapse in his design classes his response would be, “I don’t believe you because the Mothman did it!” This response comes from an expert in the field since Boeing is a local and graduated 2012 valedictorian of Gallia Academy High School which has an extremely difficult to obtain school GPA of 0.7. Boeing then went off to Wittenberg University to study physics and chemistry. He found applications to chemistry lectures that could be utilized in the real world in the field of debauchery. He used the classical concentration equation, M1 V1 = M2 V2, to calculate alcohol coefficients and cataloged the local liquor store based on cheapest booze amount per dollar. During his time as a welding engineer at OSU he has become a the resident subject matter expert on OES, Instrumented Indentation, Microhardness Mapping, and CVN analysis based on instrumentation skills acquired earlier in his academic career. In his spare time he can always be found on the golf course spending time with his beautiful girlfriend / Putter named Buttercup. Her name is Buttercup because she is known to build Boeing up just to let Boeing down.