Phase formation, thermal stability and mechanical properties of a Cu-Al-Ni-Mn shape memory alloy prepared by selective laser melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour

Phase Formation, Thermal Stability and Mechanical Properties of a Cu-Al-Ni-Mn Shape Memory Alloy Prepared by Selective Laser Melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour

Thermoelastic phase transformation in cu-al-ni shape memory

Shape memory alloys (SMA) have some exceptional properties such as the shape memory effect and the superelasticity. Both are associated with a martensitic/austenitic phase transformation. Alloys of the system Cu-Al-Ni, Cu- Zn-Al and NiTi belong to this class of material. The interest in the study of Cubased SMA arises from the fact that they are cheaper than NiTi and might achieve better properties in specific applications. Considering the presented facts, the aim of the thesis is to understand the phase transformation and its features such as the stabilization and hysteresis using thermoelastic thermodynamics and a theory of the compatibility between the austenite and martensite for the system Cu-Al-Ni. This system attracts attention of the scientific community because it is a good candidate in the application of high temperature shape memory alloys (HTSMA), working above 100 oC. Another aim of the thesis is to evaluate the mechanical and functional properties of one alloy processed by spray forming, which was selected based in on the previous study. Important correlations were observed on the thermodynamics and crystallographic compatibility with the phase transformation characteristics of the system Cu-Al-Ni, which also enabled the production of an alloy with good functional properties regarding the shape memory effect.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)As ligas com memória de forma (LMF) possuem propriedades interessantes, como o efeito de memória de forma e o efeito da pseudoelasticidade, que são advindas de uma transformação de fase do tipo austenita/martensita. Dentre as ligas que apresentam estas propriedades, encontram-se as dos sistemas Cu-Al-Ni, Cu-Zn-Al e NiTi. O interesse em estudar as ligas a base de Cu vem do fato de que estas podem apresentar certas vantagens em relação às ligas a base de NiTi, tanto pelo custo reduzido dos elementos da liga e de processamento, como pela alto potencial de atingir melhores propriedades funcionais em aplicações específicas. Considerando essas questões, o objetivo da presente tese é o entendimento das transformações de fase martensíticas termoelásticas e suas características como estabilização e histerese, através de teorias de concentração de elétrons de valência, termodinâmica de transformação termoelástica e teorias de compatibilidade das fases austeníticas e martensíticas para as ligas do sistema Cu-Al-Ni com adições de outros elementos. Este sistema é de interesse da comunidade científica pelo fato de ser um bom candidato na utilização de ligas com memória de forma a altas temperaturas (acima de 100 oC). Um segundo objetivo desta tese é a avaliação das propriedades mecânicas e funcionais de uma liga processada por conformação por spray e que foi selecionada baseando-se nos critérios estudados anteriormente. Foram observadas importantes correlações entre os fatores termodinâmicos e de compatibilidade cristalográfica aqui estudados e as características de transformação de fase em ligas do sistema Cu-Al-Ni, o que permitiu também a produção de uma liga com boas propriedades funcionais no que tange o efeito com memória de forma

New Zr-based glass-forming alloys containing Gd and Sm

The effect of minor additions of Gd and Sm on the glass-forming ability (GFA) of Cu-Zr-Al alloys is investigated here. The rationale for these additions is the fact that the atomic size distribution can increase GFA by changing the topology of the alloy as a function of cluster stability, which is tied to the electronegativity and ionic and covalent nature of alloys. Ingots with nominal compositions of Cu40Zr49Al10.5Gd0.5, Cu40Zr49Al10.5Sm0.5 and Cu39Zr50Al9Gd2 were prepared by arc-melting and rapidly quenched ribbons were produced by the melt-spinning technique. Bulk samples with a thickness of up to 10 mm were also produced by casting, using a wedge-shaped copper mold. The samples were characterized by differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy. The three compositions showed a fully amorphous structure in the ribbons and a predominantly homogeneous amorphous structure with a thickness of up to 10 mm, although some gadolinium oxide crystals as well as samarium compounds were found to be scattered in the amorphous matrix in 5-mm-thick samples. The amorphous phases in the alloys showed high thermal stability with a supercooled liquid region (ΔTx) of about 70 K

Phase Formation, Thermal Stability and Mechanical Properties of a Cu-Al-Ni-Mn Shape Memory Alloy Prepared by Selective Laser Melting

Selective laser melting (SLM) is an additive manufacturing process used to produce parts with complex geometries layer by layer. This rapid solidification method allows fabricating samples in a non-equilibrium state and with refined microstructure. In this work, this method is used to fabricate 3 mm diameter rods of a Cu-based shape memory alloy. The phase formation, thermal stability and mechanical properties were investigated and correlated. Samples with a relative density higher than 92% and without cracks were obtained. A single monoclinic martensitic phase was formed with average grain size ranging between 28 to 36 μm. The samples exhibit a reverse martensitic transformation temperature around 106 ± 2 °C and a large plasticity in compression (around 15±1%) with a typical “double-yielding” behaviour