Transient Liquid Phase Joining of Carbon and Stainless Steels to Aluminum Alloy Using Gallium Metal

THESIS ABSTRACT TRANSIENT LIQUID PHASE JOINING OF CARBON AND STAINLESS STEELS TO ALUMINUM ALLOY USING GALLIUM METAL BY Yuke Wang B.S. Chongqing University of Technology, Chongqing, China 2011 The objectives of this thesis is to develop a metallurgical understanding of joining two dissimilar metals via transient liquid phase (TLP) bonding. TLP Joining of 1020 carbon steel and 304L stainless steel to 6061-T6 Aluminum (Al) alloy were carried out using gallium (Ga) as filler metal. Joints were fabricated using different bonding temperatures and holding times. The microstructures for each sample were examined via optical microscopy and scanning electron microscopy (SEM). Tensile tests were performed for representative samples from each bonding system. Micro-hardness profile across the bonding region for each sample was also obtained. Sound joints were obtained. The brittle Fe2Al5 intermetallic compound was identified in the midst of reaction layers of the 1020 steel/Ga/6061-Al joints. The sample processed at 450oC for four hours showed the highest tensile strength of 81.0 MPa. On the other hand, no brittle intermetallic compound was identified at the bonding regions of the 304L Stainless Steel/Ga/6061-Al joints, The highest tensile strength of 100.0 MPa were measured for the samples fabricated at 330oC for six hours. It was determined that the Ga film promotes the formation of the narrow transient liquid layer that aided in the isothermal local solidification, and enhanced the inter-diffusion of the iron and aluminum atoms. The weakening of mechanical properties on 6061-Al observed from both systems is due to overaging and the embrittlement caused by excessive amount of Ga that segregated into the Al

Comparison of general data and objective image quality of patients between Group 1 (routine-dose FBP reconstruction) and Group 2 (120 KV+84 mAs/IRT L5 reconstruction).

<p>Note: ^†indicates the results of <i>x</i>². SNR: Signal-to-noise ratio, CNR: contrast-to-noise ratio.</p

Phantom images acquired with routine dose(120 kv, 210 mAs) and different low dose (120 kv, 125–63 mAs) scan.

<p>A: 120 KV, 210 mAs with FBP reconstruction. B: 120 KV, 125 mAs with iDose⁴ reconstruction (L3). C: 120 KV, 105 mAs with iDose⁴ reconstruction (L4). D: 120 KV, 84 mAs with iDose⁴ reconstruction (L5). E: 120 KV, 63 mAs with iDose⁴ reconstruction (L6). The subjective image quality score was equivalent between Group D and Group A. The score of nodule conspicuity in the Group E was significantly lower than that in the Group A.</p

Noise reduction in images reconstructed with iDOSE⁴ in phantom.

<p>At equal radiation doses, iDose⁴ reconstruction algorithm yielded lower image noise than FBP reconstruction algorithm, and with increased iDose⁴ level, image noise decreased in a linear manner.</p

Representative examples of patient scans.

<p>There were no significant differences in subjective ranking for image sharpness, contrast, noise, and overall acceptability between patients belonging to Group 1 and 2. (A, B): Group 1, CPR pictures of LAD (Fig. 5A) and RCA (Fig. 5B) of a 53-year-old male with a body mass index (BMI) of 24.2 scanned at 120 kVp and 210 mAs and reconstructed with filtered back projection. Image quality (IQ) scores were 4, 4, 4, and 4 for contrast, sharpness, subjective noise, and acceptability, respectively. (C, D): Group 2, A 57-year-old male with BMI of 24.1 scanned at 120 kVp (Fig. 5C) and 84 mAs (Fig. 5D) and reconstructed with L5. IQ scores were 4, 4, 4 and 4 for contrast, sharpness, subjective noise, and acceptability, respectively.</p

MTF curves of the phantom scans.

<p>No significant differences are observed between Group A and each of the low-dose iterative reconstruction groups (Groups B–E).</p

Subjective image quality scores for phantoms in different dose groups.

<p>FBP: filtered back projection; L: IRT level.</p

Comparison of subjective image quality between Group 1 (routine-dose FBP reconstruction) and Group 2 (120 KV+84 mAs/IRT L 5).

†<p>Mann-Whitney test were used.</p

Survey on collection, concentration, and assay methods for environmental surveillance of S. Typhi.

(DOCX)</p

Total and operational costs per sample.

Table A in S3 Text. Total and operational costs per sample (modeled). (DOCX)</p