Fatigue crack behavior on a Cu-Zn-Al SMA

Abstract

In recent years, mechanical property of many SMA has improved in order to introduce these alloys in specific field of industry. Main examples of these alloys are the NiTi, Cu-Zn-Al and Cu-Al-Ni which are used in many fields of engineering such as aerospace or mechanical systems. Cu-Zn-Al alloys are characterized by good shape memory properties due to a bcc disordered structure stable at high temperature called β-phase, which is able to change by means of a reversible transition to a B2 structure after appropriate cooling, and reversible transition from B2 secondary to DO3 order, under other types of cooling. In β-Cu-Zn-Al shape memory alloys, the martensitic transformation is not in equilibrium at room temperature. It is therefore often necessary to obtain the martensitic structure, using a thermal treatment at high temperature followed by quenching. The martensitic phases can be either thermally-induced spontaneous transformation, or stressinduced, or cooling, or stressing the β-phase. Direct quenching from high temperatures to the martensite phase is the most effective because of the non-diffusive character of the transformation. The martensite inherits the atomic order from the β-phase. Precipitation of many kinds of intermetallic phases is the main problem of treatment on cu-based shape memory alloy. For instance, a precipitation of α-phase occurs in many low aluminum copper based SMA alloy and presence of α-phase implies a strong degradation of shape recovery. However, Cu-Zn-Al SMA alloys characterized by aluminum contents less than 5% cover a good cold machining and cost is lower than traditional NiTi SMA alloys. In order to improve the SMA performance, it is always necessary to identify the microstructural changing in mechanical and thermal conditions, using X-Ray analyses. In this work a Cu-Zn-Al SMA alloy obtained in laboratory has been microstructurally and metallographically characterized by means of X-Ray diffraction and Light Optical Microscope (LOM) observations. Furthermore a fatigue crack propagation and fracture surface scanning electron microscope (SEM) observations have been performed in order to evaluate the crack path and the main crack micromechanisms.

Improving the Models of Dynamics of Adaptively Controlled Elements and Drives Based on Functional Materials

“…The algorithm for solving these inequalities acts as an adaptation algorithm, the meaning of which is to form acceptable estimates of τ unknown parameters x. If inequalities (7) are violated for some τ = τ(t), then this indicates the unsatisfactoriness of the current estimate τ(t) and the need for its correction. If inequalities (7) are satisfied, this indicates the acceptability of both the estimates themselves and the adaptive control law synthesized on their basis.…”

“…Based on the empirical evidence of worldwide research in using materials with SME, technological methods of their processing in conjunction with the operational capabilities has supported the hypothesis of the need for thermal-force cycling in the pre-deformation state to be developed [6][7][8].…”

Evolución de la fase α en una serie de aleaciones Zn-Al-Cu de acuerdo a su tamaño y propiedades mecánicas generadas por el aumento de Cu y el proceso de envejecido

“…La transformación de las fases de las aleaciones Al-Cu-Zn por medio del porcentaje químico o por diferentes tratamientos térmicos, determina importantes cambios en sus propiedades mecánicas (Flores Ramos et al, 2014). Incluso son aleaciones útiles en aplicaciones aeroespaciales (Di Cocco et al, 2014).…”

Novel zinc-based alloys used to improve the corrosion protection of metallic substrates

“…The inner phase, named  phase, is a hexagonal phase, characterized by iron content equal to about 7-12% by weight (7)(8)(9)(10)(11)(12) wt%).…”

“…high temperature at contact of the bath surface (bath temperature equal to 460±2°C)[9].Two different types of improved zinc-based coated specimens are analysed, with a coating obtained employing either a 3% in weight tin addition (named Series 1 specimens), or a 5% in weight aluminium, 1% in weight tin, 0.5% in weight copper addition (named Series 2 specimens).…”