Projeto e fabricação de ligas de alta entropia do sistema Al-Co-Cr-Fe-Ni-V: caracterização microestrutural e mecânica com avaliação das resistências ao desgaste e à corrosão
Data
2024-10-29
Autores
Souto, Carlos Alberto 
Orientadores
Cardoso, Kátia Regina
Tipo
Tese de doutorado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
As crescentes demandas por materiais com propriedades excepcionais, como alta resistência mecânica, elevada resistência ao desgaste e à corrosão, têm impulsionado o estudo e desenvolvimento das ligas de alta entropia (LAEs), reconhecidas por suas propriedades e amplo potencial de aplicação estrutural. Este trabalho concentra-se na concepção e caracterização de LAEs no sistema Al-Co-Cr-Fe-Ni-V, visando aplicações que demandem uma combinação de alta resistência mecânica, desempenho tribológico e resistência à corrosão. As composições foram projetadas com base em simulações termodinâmicas, pelo método CALPHAD, visando obter soluções sólidas simples, formadas majoritariamente por fases cúbicas de corpo centrado (CCC). Foram estudadas as ligas Al16,7Co16,7Cr16,7Fe16,7Ni16,7V16,7, Al30Co30Cr5Ni30V5, Al20Co10Cr20Fe20Ni20V10, Al20Co5Cr20Ni35V20, Al35Co25Cr10Ni25V5 e Al35Co15Cr20Fe10Ni15V5 (% at.), fabricadas por fusão em forno a arco elétrico e submetidas a tratamentos térmicos. Os resultados demonstraram que as ligas apresentaram microestruturas bifásicas, predominantemente compostas pelas fases A2 e B2. Difratometria de raios X e microscopia eletrônica de varredura confirmaram as previsões de fases calculadas, porém revelaram variações microestruturais em função da composição e do tratamento térmico. Os resultados dos ensaios de dureza evidenciaram a heterogeneidade microestrutural das ligas, com valores médios de 500 HV a 735 HV na condição bruta de fusão e 470 HV a 680 HV após os tratamentos térmicos. Testes de desgaste indicaram coeficientes de desgaste competitivos se comparadas a muitas LAEs já relatadas na literatura, apresentando os coeficientes de desgaste entre 1,4.10⁻6 mm³/N.m e 5,4.10⁻6 mm³/N.m. Com relação aos testes de corrosão, as LAEs apresentaram taxas de corrosão com valores alinhados e, na maioria das ligas, superiores ao aço inoxidável 316L (6,5.10⁻³ mm/ano). Entre as ligas avaliadas, destacou-se a Al30Co30Cr5Ni30V5, que apresentou a menor densidade de corrente de corrosão (6,8.10⁻1 𝜇A/cm²), menor taxa de corrosão (2,5.10⁻³ mm/ano) e comportamento passivo estável, demonstrando alta resistência à corrosão localizada.
The increasing demand for materials with exceptional properties, such as high mechanical strength, enhanced wear resistance, and corrosion resistance, has driven the study and development of high-entropy alloys (HEAs), recognized for their outstanding properties and broad potential for structural applications. This study focuses on the design and characterization of HEAs within the Al-Co-Cr-Fe-Ni-V system, targeting applications that require a combination of high mechanical strength, tribological performance, and corrosion resistance. The compositions were designed based on thermodynamic simulations using the CALPHAD method, aiming to obtain simple solid solutions predominantly composed of body-centered cubic (BCC) phases. The studied alloys include Al16,7Co16,7Cr16,7Fe16,7Ni16,7V16,7, Al30Co30Cr5Ni30V5, Al20Co10Cr20Fe20Ni20V10, Al20Co5Cr20Ni35V20, Al35Co25Cr10Ni25V5 e Al35Co15Cr20Fe10Ni15V5 (at.%). These alloys were fabricated by arc melting and subjected to heat treatments. The results revealed biphasic microstructures, predominantly composed of A2 and B2 phases. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the calculated phase predictions, while also revealing microstructural variations as a function of composition and heat treatment. Hardness measurements highlighted the microstructural heterogeneity of the alloys, with average values ranging from 500 HV to 735 HV in the as-cast condition and 470 HV to 680 HV after heat treatments. Wear tests indicated competitive wear coefficients compared to many HEAs reported in the literature, with wear coefficients ranging from 1.4 × 10⁻⁶ mm³/Nm to 5.4 × 10⁻⁶ mm³/Nm. Regarding corrosion tests, the HEAs exhibited corrosion rates comparable to or exceeding those of 316L stainless steel (6.5 × 10⁻³ mm/year) in most alloys. Among the evaluated alloys, Al30Co30Cr5Ni30V5 stood out with the lowest corrosion current density (6.8 × 10⁻¹ µA/cm²), the lowest corrosion rate (2.5 × 10⁻³ mm/year), and stable passive behavior, demonstrating superior localized corrosion resistance.
The increasing demand for materials with exceptional properties, such as high mechanical strength, enhanced wear resistance, and corrosion resistance, has driven the study and development of high-entropy alloys (HEAs), recognized for their outstanding properties and broad potential for structural applications. This study focuses on the design and characterization of HEAs within the Al-Co-Cr-Fe-Ni-V system, targeting applications that require a combination of high mechanical strength, tribological performance, and corrosion resistance. The compositions were designed based on thermodynamic simulations using the CALPHAD method, aiming to obtain simple solid solutions predominantly composed of body-centered cubic (BCC) phases. The studied alloys include Al16,7Co16,7Cr16,7Fe16,7Ni16,7V16,7, Al30Co30Cr5Ni30V5, Al20Co10Cr20Fe20Ni20V10, Al20Co5Cr20Ni35V20, Al35Co25Cr10Ni25V5 e Al35Co15Cr20Fe10Ni15V5 (at.%). These alloys were fabricated by arc melting and subjected to heat treatments. The results revealed biphasic microstructures, predominantly composed of A2 and B2 phases. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the calculated phase predictions, while also revealing microstructural variations as a function of composition and heat treatment. Hardness measurements highlighted the microstructural heterogeneity of the alloys, with average values ranging from 500 HV to 735 HV in the as-cast condition and 470 HV to 680 HV after heat treatments. Wear tests indicated competitive wear coefficients compared to many HEAs reported in the literature, with wear coefficients ranging from 1.4 × 10⁻⁶ mm³/Nm to 5.4 × 10⁻⁶ mm³/Nm. Regarding corrosion tests, the HEAs exhibited corrosion rates comparable to or exceeding those of 316L stainless steel (6.5 × 10⁻³ mm/year) in most alloys. Among the evaluated alloys, Al30Co30Cr5Ni30V5 stood out with the lowest corrosion current density (6.8 × 10⁻¹ µA/cm²), the lowest corrosion rate (2.5 × 10⁻³ mm/year), and stable passive behavior, demonstrating superior localized corrosion resistance.