Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys

Nickel-Titanium (Ni-Ti) shape memory alloys (SMAs) have been used in many engineering and medical applications. However, their use is limited, due to their low transformation temperatures, difficulties in processing and high cost of the raw materials. As an alternative material to Ni-Ti alloys, copp...

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Main Author:	Saud, Safaa Najah
Format:	Thesis
Language:	English
Published:	2014
Subjects:	TJ Mechanical engineering and machinery
Online Access:	http://eprints.utm.my/id/eprint/77887/1/SafaaNajahSaudPFKM2014.pdf
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spelling	my-utm-ep.778872018-07-18T04:11:11Z Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys 2014-11 Saud, Safaa Najah TJ Mechanical engineering and machinery Nickel-Titanium (Ni-Ti) shape memory alloys (SMAs) have been used in many engineering and medical applications. However, their use is limited, due to their low transformation temperatures, difficulties in processing and high cost of the raw materials. As an alternative material to Ni-Ti alloys, copper-based alloys are successfully being used. Among copper-based SMAs, Cu-Al-Ni alloys are used in a wide range of applications, particularly if high temperatures are required. However, Cu-Al-Ni SMAs also have limitations such as very low ductility and low shape recovery strain. Therefore, this research aims to enhance the ductility and shape memory effect of Cu-Ni-Al by alloying additions and aging heat treatment. The base metal, Cu-Al-Ni, was cast without and with different amounts of the fourth alloying elements, namely, titanium (Ti), manganese (Mn) and cobalt (Co). The modified and unmodified alloys were homogenized and aged at 373 K, 423 K and 523 K for 24 and 48 hours. Phase transformation and microstructural changes were characterized using techniques such as optical microscopy, field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), differential scanning calorimetry (DSC), x-ray diffractometry (XRD) and transmission electron microscopy (TEM). The tensile properties and hardness were determined using a universal Instron tensile machine and Vicker‟s hardness test machine, respectively. The shape memory test was performed using a specially designed tensile machine equipped with a heating tape. The results revealed that the alloying elements and aging treatment were found to control the phase morphology, orientations and grain size along with the formation of precipitates, thereby improving the shape memory characteristics, ductility and hardness. The volume fraction, size and distribution of the precipitates are mainly dependent on the type and amount of alloying element as well as the condition of aging treatment. The Cu-Al-Ni with the addition of 0.76 wt. % Ti and age treated showed complete recovery after the shape memory test. This may be attributed to the high volume of X-phase precipitates and grain refinement that led to the restricted mobility of martensite variant interfaces and dislocations. It was found that the alloy with 1.14 wt. % of Co gave the best overall improvement in terms of the transformation temperatures, ductility and shape memory recovery. These improvements were mainly due to the exceptionally high content of the gamma-2 (γ2) phase in the microstructures of the modified alloy. Furthermore, the ductility of the Cu-Al-Ni SMAs increased from 1.65 to 7.0 % when 1.14 wt. % Co was added and the alloy undergone aging treatment where the fracture surfaces showed more ductile features and less brittle cleavages. It was also found that Cu-Al-Ni SMAs with 1.14 wt. % Co obtained full shape recovery after being aged at 523 K for 48 hours. 2014-11 Thesis http://eprints.utm.my/id/eprint/77887/ http://eprints.utm.my/id/eprint/77887/1/SafaaNajahSaudPFKM2014.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:109660 phd doctoral Universiti Teknologi Malaysia, Faculty of Mechanical Engineering Faculty of Mechanical Engineering
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	TJ Mechanical engineering and machinery
spellingShingle	TJ Mechanical engineering and machinery Saud, Safaa Najah Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys
description	Nickel-Titanium (Ni-Ti) shape memory alloys (SMAs) have been used in many engineering and medical applications. However, their use is limited, due to their low transformation temperatures, difficulties in processing and high cost of the raw materials. As an alternative material to Ni-Ti alloys, copper-based alloys are successfully being used. Among copper-based SMAs, Cu-Al-Ni alloys are used in a wide range of applications, particularly if high temperatures are required. However, Cu-Al-Ni SMAs also have limitations such as very low ductility and low shape recovery strain. Therefore, this research aims to enhance the ductility and shape memory effect of Cu-Ni-Al by alloying additions and aging heat treatment. The base metal, Cu-Al-Ni, was cast without and with different amounts of the fourth alloying elements, namely, titanium (Ti), manganese (Mn) and cobalt (Co). The modified and unmodified alloys were homogenized and aged at 373 K, 423 K and 523 K for 24 and 48 hours. Phase transformation and microstructural changes were characterized using techniques such as optical microscopy, field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), differential scanning calorimetry (DSC), x-ray diffractometry (XRD) and transmission electron microscopy (TEM). The tensile properties and hardness were determined using a universal Instron tensile machine and Vicker‟s hardness test machine, respectively. The shape memory test was performed using a specially designed tensile machine equipped with a heating tape. The results revealed that the alloying elements and aging treatment were found to control the phase morphology, orientations and grain size along with the formation of precipitates, thereby improving the shape memory characteristics, ductility and hardness. The volume fraction, size and distribution of the precipitates are mainly dependent on the type and amount of alloying element as well as the condition of aging treatment. The Cu-Al-Ni with the addition of 0.76 wt. % Ti and age treated showed complete recovery after the shape memory test. This may be attributed to the high volume of X-phase precipitates and grain refinement that led to the restricted mobility of martensite variant interfaces and dislocations. It was found that the alloy with 1.14 wt. % of Co gave the best overall improvement in terms of the transformation temperatures, ductility and shape memory recovery. These improvements were mainly due to the exceptionally high content of the gamma-2 (γ2) phase in the microstructures of the modified alloy. Furthermore, the ductility of the Cu-Al-Ni SMAs increased from 1.65 to 7.0 % when 1.14 wt. % Co was added and the alloy undergone aging treatment where the fracture surfaces showed more ductile features and less brittle cleavages. It was also found that Cu-Al-Ni SMAs with 1.14 wt. % Co obtained full shape recovery after being aged at 523 K for 48 hours.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Saud, Safaa Najah
author_facet	Saud, Safaa Najah
author_sort	Saud, Safaa Najah
title	Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys
title_short	Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys
title_full	Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys
title_fullStr	Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys
title_full_unstemmed	Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys
title_sort	influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of cu-al-ni shape memory alloys
granting_institution	Universiti Teknologi Malaysia, Faculty of Mechanical Engineering
granting_department	Faculty of Mechanical Engineering
publishDate	2014
url	http://eprints.utm.my/id/eprint/77887/1/SafaaNajahSaudPFKM2014.pdf
_version_	1747817855417581568

Influence of alloying elements and aging treatment on the phase transformation and shape memory behavior of Cu-Al-Ni shape memory alloys

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