Banca de QUALIFICAÇÃO: CÁSSIA CARLA DE CARVALHO

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : CÁSSIA CARLA DE CARVALHO
DATE: 08/12/2022
TIME: 10:00
LOCAL: Sala virtual (videoconferência): https://meet.google.com/kct-udcq-nre
TITLE:

Analysis of thermal variables, microstructure and mechanical strength of directionally solidified Sn-34wt.%Bi-xZn alloys

KEY WORDS:

Directional solidification; Thermal parameters; Sn-Bi-Zn alloys; Microstructure; Mechanical properties.

PAGES: 116
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Metalurgia Física
SPECIALTY: Transformação de Fases
SUMMARY:

Due to environmental and human health issues related to the use of lead-containing alloys for applications in soldered joints of electronic microcomponents, it is necessary to study new soldering alloys with less toxicity and similar properties to the Sn-Pb system alloys. In this sense, Sn-Bi alloys have emerged as promising alternatives, since they have high mechanical strength and creep, low cost and low coefficient of thermal expansion (CTE), however, such alloys exhibit such as coarsening of the microstructure during thermal aging, low wettability on metallic substrates and low ductility. One way to improve such characteristics is to add ternary alloying elements such as zinc (Zn), which can refine the microstructure, increase mechanical properties and inhibit Bi segregation in Sn-Bi alloys. In this sense, the present proposal aims to assess the effect of Zn (0.5% and 9% by weight) additions on the microstructure, thermal parameters (cooling rate-Ṫ_L and growth rate-V_L), segregation and mechanical properties of directionally solidified Sn-34wt.%Bi-xZn alloys under unsteady state conditions. For this, the samples have been characterized by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD), in addition to mechanical tests such as Vickers microhardness and tensile. Thermodynamic simulations via Thermo-calc have been performed to obtain information such as transformation temperatures, solidification paths, types of phases and their fractions. The microstructure for Sn-Bi-Zn alloys is completely dendritic, composed of an Sn-rich matrix (β-Sn) with Bi precipitates (with spherical, ellipsoidal and plate-type morphologies) in its interior and surrounded by a eutectic mixture of the Sn and Bi phases predominantly in the coarse scale, with the Sn-34wt.%Bi-9wt.%Zn alloy exhibiting Zn primary needles. The addition of 9wt.%Zn promoted a slight increase in Ṫ_L and V_L values. The Zn additions caused a coarsening of the dendritic arrangement, except for the tertiary dendritic spacing for the Sn-34wt.%Bi-0.5wt.%Zn alloy. The Zn content remained constant throughout the Sn-34wt.%Bi-0.5wt.%Zn casting, while for the alloy with 9wt.%Zn addition, it presented a normal type macrosegregation profile. Zn additions caused inverse-type macrosegregation profiles for the bismuth, differing from the Sn-Bi binary alloy. The additions of Zn promoted an increase in Vickers microhardness and yield strength (σ_y) and ultimate tensile strength (σ_u), mainly for more refined microstructures, however, not reflecting on specific elongation values (δ). The Sn-34wt.%Bi-0.5wt.%Zn and Sn-34wt.%Bi-9wt.%Zn alloys exhibit ductile and brittle, and brittle (cleavage) fracture modes, respectively.

COMMITTEE MEMBERS:
Presidente - 2345599 - BISMARCK LUIZ SILVA
Externo ao Programa - 1652765 - MAURÍCIO MHIRDAUI PERES - UFRNExterno ao Programa - 2414250 - MEYSAM MASHHADIKARIMI - UFRN