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Study of corrosion and dry Study of corrosion and dry sliding wear resistance for sliding wear resistance for

copper based shape copper based shape memory alloysmemory alloys

By Aseel safee hemza

Al- dulamy B.SC

Supervised by Dr. Abdul Raheem . K. Abid Ali

IntroductionIntroduction

Shape-memory alloys are a new class of functional materials have an abil i ty to recover a particular shape with changing temperature. for example Ag-Cd , Au-Cd , Cu-Al-Ni, Cu-Sn , Cu-Zn-(X) ,Ni-Al, Ni-Ti, Fe-Pt, Mn-Cu and Fe-Mn-Si alloys , are a group of metall ic materials . The temperature in which phase transformation occurs, is called the transformation temperature.

COOLING

APPLIED STRESS HEATING

TypesTypesSmart material May be divide to :-Smart material May be divide to :-- smart color-changing materials / such as - smart color-changing materials / such as photochromics , thermochromic , mechanochromic and photochromics , thermochromic , mechanochromic and chemochromic. chemochromic. - smart materials- energy – changing/ such as - smart materials- energy – changing/ such as Light – emitting materials,Electroluminescence, Light – emitting materials,Electroluminescence, Semiconductor phenomena and Shape Memory Alloys.Semiconductor phenomena and Shape Memory Alloys.

Mechanism of the Shape Memory Alloys - martensite results from the solid state process of martensitic transformation and the reaction is displacive , no change in chemical composition or atomic diffusion. - Martensitic reactions normally occur athermally and martensite is formed upon cooling from a higher temperature phase called the parent phase. This phenomna come from two shear directions can be applied to the squares to produce two different rhombus variants .

Transformation Behavior of Shape Memory Alloys

transformation behavior classified according to the type of effect, shape memory effect caused by temperature induced martensitic transformation while pseudo-elasticity (also called superelasticity) happens because of stress induced martensitic transformation (SIMT). Shape memory effect divided to:- -One way shape memory effect.-Two way shape memory effect-pseudo-elasticity

One-way shape memory effect

Austenite cooled to the Martensite , deformation of the twinned-martensite leads to microstructural changes (detwinning), making possible macroscopic strains of up to 10 %. heating causes the reverse transformation into Austenite. original shape retained during cooling because of accommodation processes (repeated twinning).

Two-way shape memory effect Remember both hot and cold shapes. They can be cycled

between two different shapes without the need of external stress. Shapes changes occur under the influence of internal stress. Self–accommodation of the martensite microstructure is lost in the two–way effect due to the presence of these internal stresses.

Pseudoelasticity pseudoelasticity describes a mechanical memory

has the ability to return to its predetermined shape after a (local) deformation of up to 10 % without heating, just by unloading (rubber-like behavior). observed if the Austenite is stabilized to operation temperature by specific alloying and/or heat treatment. The explanation of this phenomenon is a stress-induced phase transformation during loading and unloading.

APPLICATIONAPPLICATION

• Aerospace and Naval ApplicationsAerospace and Naval Applications• Smart Bridges Smart Bridges • Sensors Sensors • Actuators Actuators • Medical Medical

– DentistryDentistry– TweezersTweezers

• Mobile Telephone Mobile Telephone • ClothingClothing

Martensit ic transformationMartensit ic transformation

Stress-induced transformations Thermally induced transformations

Magnetic field-induced transformations Electric field-induced transformations

Problems in shape memory alloys Problems in shape memory alloys Shape memory alloys undergoes to corrosion and wear as Shape memory alloys undergoes to corrosion and wear as

shown in the figure by the movement of the fluid in the coil of shown in the figure by the movement of the fluid in the coil of shape memory alloy as well as the movement of the fluid and shape memory alloy as well as the movement of the fluid and the applied pressure causes wear and erosion for the surface of the applied pressure causes wear and erosion for the surface of the alloy. Other example the shower valve that is undergoes to the alloy. Other example the shower valve that is undergoes to corrosion and wear . corrosion and wear .

Memory-safe -antiscald shower valve.Oilcooler bypass valve

Technological routineTechnological routine

Powder preparation

MixingBest

compacting stress

Density Test Compaction

Heat Treatments

Sintering-quenching

Tests PorosityXRD TestDSC test for

quenched samples

Tests

Chemical Test

Mechanical

TestsMicroscope

Observation

SME Test

HardnessWear Test

SEM TestOptical

Microscope

Tafel Corrosion

TestEDS Test

2 hr at 550 oC

1 hr at 900 oC

Tem

pera

tur

(Oc)

Times (hr)

Sintering process

Quenching process

1 hr at 850 OC

2-4 oCTem

oera

ture

(o C

)

Time (hr)

Corrosion test The corrosive behavior of Cu–Al–Ni shape memory alloy in solution of (3.5gmNaCl) or (5gm NaOH) at room temperature was studied by means of open circuit potential measurements and investigated by Tafel extrapolation that is used to estimate corrosion current

Tafel corrosion curve for alloy (Cu11Al4Ni0.6Cr)in NaOH solution.

Wear test

wear instrument

Dry sliding wear behavior has been studied by using pin on disk concept using (950 rpm) and constant sliding distance(6.3cm) with ( 4.9N and10N) load After a period of time (5,10 and 15 min.)

ResultsResults: : • Best compression was (520Mpa) and the XRD results

of sintered alloys shown formation (Al4Cu9),(Cu9Al4) and for quenched samples formed (AlCu3)

• The apparent and true porosity decreases with pressure .

• Rockwell hardness values for alloys increased with alloying elements and the values of the hardness for martensite phase greater than the hardness for sintered state .

• DSC thermogram of quenched sample alloy(Cu11Al4Ni0.6Cr) shown that the As ,Af through the range (280oC-320oC). And for quenched sample alloy(Cu11Al4Ni0.6Ag) the As , Af through the range (271.0oC-321OC).

• SEM microstructure of the quenched alloys surface refer to formation martensites lines

• Among the alloys, quenched alloy (Copper-13%Aluminum-4% Nickel-0.9% Ag) has the lowest

corrosion current (2.7μA) then has the highest corrosion resistance in NaCl solution and quenched alloy(Copper-13%Aluminum-4%Nickel-0.9%Cr) has

the lowest corrosion current (24.08μA)in NaOH solution and quenched alloy(Cu-13%wt.Al-4%wt.Ni-

0.9%Cr)has the highest wear resistance and the volume loss was (2.1919mm3) .

Conclusions:• X-ray diffraction analysis shows that the sintering at 550oC for

2hr. followed by sintering at 900oC for 1hr in vacuum of (10-4

torr) is efficient to satisfy sintering process in which elemental powders are completely transformed into alloy structure.

• Martensitic transformation is occurred in (Cu-Al-Ni) based shape memory alloys completely by direct quenching form 850oC into ice water(2-4oC ) as clearly shown from x-ray diffraction analysis.

• The alloys tend to form intermetallic compounds (Al4Cu9), (Cu9Al4) for alloys in sintering state , also (AlCu3)phase formed in quenching state for alloy(2) and alloy (10).

• Corrosion current of the quenched alloys is less than that for sintered alloys .

• The EDX analysis revealed the presence of copper ,aluminum ,Nickel , Chromium , Oxides and Chlorides on the alloy surface.

• The wear resistance for the alloys increases with the increase in alloying elements and weight loss increases with increasing of normal load.

• The tafel curve can be characterized by one anodic current density peak and the cathodic current density peak.

• Corrosion current has been decreased with increasing the percent of alloying elements (Cr or Ag) .

Suggestions and Recommendation

• In order to increase density of sintered compacts, double action press or hot isostatic pressing should be used.

• Transmission electron microscopy (TEM) and high resolution of (SEM) should be used to reveal the structure of martensite, its form and the degree of ordering for obtained martensite .

• The solution of corrosion should be tested after corrosion process in order to estimation ions concentration.