Rapid solidification and advanced

manufacturing of Cu-based shape memory

alloys with complex geometries

Piter Gargarella, Claudio S. Kiminami, Walter J. Botta, Alberto M. Jorge Jr. and Claudemiro Bolfarini

Federal University of São Carlos (UFSCar), Department of Materials Engineering (DEMa), Brazil

Simon Pauly and Tobias Gustmann

Institute for Complex Materials, IFW-Dresden, Germany

Slide 2

Contents

I. Motivation

- Why Cu-based SMAs and rapid solidification?

I. Project details/ project partners

- Project coordination

- Aim and project duration

- Summary of scientific outputs

III. Results

- Spray forming of Cu-based SMAs

- Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

Slide 3

Motivation

youtube.com/watch?v=0K1niBUyAqY

The shape memory effect

Slide 4

Motivation

• Exhibit martensitic

transformation: the material

changes its structure, from a

low symetry structure

(martensite), stable at ↓T, to

a high simetric structure

(austenite), stable at ↑T.

• Shape Memory Effect.

• These alloys can show

superelasticity or

pseudoplasticity: large

recoverable strain up to 10 %.

K. Otsuka and K. Shimizu, International Metals Reviews (1986)

Shape memory effect

T TT

martensiteaustenite

Superelastic behaviour of a TiNi wire

J. Mohd Jani et al. Mat. and Design 56 (2014) 1078–11134

Slide 5

C. Cismasiu (ed.) Shape memory alloys, Rijeka:Sciyo, 2010

Active Bending Catheter

Ortodontic applications

Stent

Simon filter

Motivation

Slide 6

Cryofit

C. Cismasiu (ed.) Shape memory alloys, Rijeka:Sciyo, 2010M.H. Wu, L.M. Schetkz, Procedings of the ICSMT, 2000

Flexible Glasses

Rice cooker

Turbines

Car parts

Motivation

Slide 7

Motivation

• Cu-based vs TiNi-based

•Cu-based SMAs: good SM behaviour, higher thermal and eletricalconductivity, lower cost and are easier to process than traditional TiNi-based SMAs.

•Cu-Al-Ni: interesting for high temperature applications (100-200 oC).

•Coarse-grained Cu-based SMAs are intrinsically brittle

• Elastic anisotropy transgranular fracture

• Grain refinement: grain refiners (e.g. Ti, Zr, B, …), thermo-mechanical treatment, cooling rate

• Rapid solidification : avoid the formation of eq. phases: α, γ2 and NiAl.

• Novel methods: atomization, spray forming and sel. laser melting

• Selective laser melting: explore the effect of geometry

Cu-14Al-3.9Ni

Cu-14.9Al-4.1Ni

Cu-14Al-4Ni

Cu-13.2Al-3.8Ni

S. Miyazaki, Trans JIM 1981

loaded unloaded

Slide 8

8

Phase 1 (01.01.2013 – 31.03.2015):

i) Produce Cu-based SMAs by spray forming and gas atomisation;

ii) Use SLM to consolidate the powders obtained;

iii) Characterize the samples produced.

Phase 2 (01.08.2016 – 31.07.2020):

i) Optimize SLM, atomization and spray forming process parameters;

ii) Investigate the formation of oligocrystalline structures by SLM;

iii) Understand the transformation behaviour by means of thermal and mechanical treatments.

Aim and Project Duration

Project details/ project partners

Slide 9

9

Rapid Solidification and advanced manufacturing of Cu-based shape

memory alloys with complex geometry

Expertise in the field of spray forming/gas atomisation

Long-standing experience regarding the investigation and characterisation of metastable materials and their thermo-mechanical properties

Know-how in terms of selective laser melting

+

Dr. S. Pauly

T. Gustmann, PhD stud.

Prof. Dr.-Ing. Piter Gargarella

Prof. Dr.-Ing. Cláudio S. Kiminami

Prof. Dr. Walter José Botta Filho

Prof. Dr.-Ing. Claudemiro Bolfarini

Prof. Dr. Alberto M.Jorge Jr.

Dr. Régis Cava, Post-doctorate

Murillo Romero, PhD stud.

Witor Wolf, PhD stud.

Rodolfo Batalha, PhD stud.

Bianca C. Arantes, undergrad.

Student

Project details/ project partners

Slide 10

Project details/ project partners

-Exchange of samples and results

-Exchange of six students (4 intern. undergrad. + 2 master/PhD thesis)

-3 PhD dissertations + 2 Master thesis

-Several visits to São Carlos/ Dresden (2 Germany → Brazil, 7 Brazil →

Germany)

-Participation in conferences (> 15) + publications (10)

Project outputs:

Slide 11

Spray Forming

• The gas atomizer a melt stream producing droplets that are colected by a substrate producing a deposit.

• Higher cooling rates during solidification:smaller grains with a lower level of microstructural segregation.

• Mean parameters:- Massic Gas/Metal ratio (GMR);- Fligh droplets distance;- Gas pressure;- Nooze design and dimensions- Shape and material´s substrate and

its movement.

Spray forming of Cu-based SMAs

Slide 12

Parameters used during spray forming

Parameter Cu-11.85Al-3.2Ni-3Mn Cu-11.35Al-3.2Ni-3Mn-0.5ZrAmount of material 5.2 kg 7.8 Kg

Liquidus temperature 1060 °C 1160 °CEjection temperature 1280 °C 1310 °C

Gas N2 N2

Atomisation pressure 0.5 MPa 0.5 MPaDiameter of nozzle 6 mm 6 mm

Flight distance 380 mm 380 mmGas-to-metal ratio (GMR) 1.94 1.94

Substrate rotation 60 rpm 60 rpm

Spray forming of Cu-based SMAs

Slide 13

Effective diameter and height of 150 mm and 75 mm respectively.

Sketch of the transversal section indicating the analyzed regions: Bottom. central and peripheral

regions.

Cu-11.85Al-3.2Ni-3Mn (%wt)

Cu-11.35Al-3.2Ni-3Mn-0.5Zr (wt%)

Spray forming of Cu-based SMAs

R. Cava, P. Gargarella et. al. submitted to Acta Materialia 2017

Slide 14

• Only the monoclinic martensite β’ phase (zigzag morphology)was observed.

• nanometric twins.

• Dureza: 190 ± 15 HV1.0

• Equiaxed grains with size of 135 ± 20 μm. Porosity around 0.87 ±0.09.

Cu-11.85Al-3.2Ni-3Mn (%wt)

100 nm

Spray forming of Cu-based SMAs

R. Cava, P. Gargarella et. al. submitted to Acta Materialia 2017

Slide 15

Cu-11.35Al-3.2Ni-3Mn-0.5Zr (wt%)

• Monoclinic martensite β’ phase (zigzag morphology) formed togetherwith a Cu-rich phase at the grain boundary.

• Equiaxed grains with size around 28.7 ± 1.5 μm. Porosity around 0.03± 0.04.

• Dureza: 361 ± 10 HV1.0

• Nanometer-sized martensitic laths, around five times smaller than theobserved for the Cu-11.85Al-3.2Ni-3Mn alloy.

Spray forming of Cu-based SMAs

R. Cava, P. Gargarella et. al. submitted to Acta Materialia 2017

Slide 16

DS

C (

a.u

.)

← cooling

heating →

Temperature (⁰C)

DS

C h

ea

tfl

ow

(a.u

.) e

xo As

Af

Mf Ms

Spray forming of Cu-based SMAs

Slide 17

17

Sample Fracture strength (MPa) Yield strength (MPa) Fracture Strain (%)

CP1 550 298 4.0

CP2 525 296 3.9

CP3 500 240 4.1

Mean/Std. Dev. 525 ± 25 278 ± 33 4.00 ± 0.1

Ref [1] 380 - 560 200 4.5 - 5.5

Ref [2] 625 280-300 6 – 7

[1] Roh et al., Materials Science and Engineering, 1991.[2] Morris et al., Acta metall, mater., 1994.

Cu-11.85Al-3.2Ni-3Mn (%wt)

Spray forming of Cu-based SMAs

R. Cava, P. Gargarella et. al. submitted to Acta Materialia 2017

Slide 18

Cu-11.35Al-3.2Ni-3Mn-0.5Zr (wt%)

18

Sample Fracture strength (MPa) Yield strength (MPa) Fracture Strain (%)

Tambient - 1 980 380 5.25

Tambient - 2 950 350 5.05

Mean/Std. dev. 965 ± 21 365 ± 21 5.1 ± 0.1

[Ref 1] Tambient 750 200 7.5 – 8.0

[Ref 2] Tambient 625 280-300 6 – 7

T= 220 °C 880 600 6.65

[Ref 2] T = 200 °C 750-800 270-280 7-8

[1] Roh et al., Materials Science and Engineering, 1991.[2] Morris et al., Acta metall, mater., 1994.

Spray forming of Cu-based SMAs

R. Cava, P. Gargarella et. al. submitted to Acta Materialia 2017

Slide 19

Microstructure of Cu-11.35Al-3.2Ni-3Mn-0.5Zr (wt%) after heat Treatment at 850 °C/30 min

Spray forming of Cu-based SMAs

Grain size:32.5 ±5 μm

Hardness (HV1.0): 284 ± 10

R. Cava, P. Gargarella et. al. submitted to Acta Materialia 2017

Slide 20

Microstructure of Cu-11.35Al-3.2Ni-3Mn-0.5Zr (wt%) after heat Treatment at 850 °C/30 min

Spray forming of Cu-based SMAs

Slide 21

200 nm

ElementNominal

composition Matrix Precipitate

Cu 81.95 83.67 76.73

Al 11.35 8.03 8.13

Ni 3.20 3.33 5.71

Mn 3.00 3.37 2.38

Zr 0.50 1.60 7.05

Total 100.0 100.0 100.0

Microstructure of Cu-11.35Al-3.2Ni-3Mn-0.5Zr (wt%) after heat Treatment at 300 °C/1 day

Y phase: Cu2AlZr cubic

Spray forming of Cu-based SMAs

Grain size: Hardness (HV1.0): 27 ± 3 μm 368 ± 9

Slide 22

2250 100 150 200

Temperature (ºC)

DS

C (

a.u

.)

-120 -70 -20 30 80 130

Temperature (ºC)

DS

C (

a.u

.)

ConditionHT Time

(Min)As(ºC)

Af (ºC)

Ms (ºC)

Mf (ºC)

Af - Ms (ºC)

As-cast - 84.4 161.6 105.9 49.3 55.7

300 ºC 1440 -4.4 36.7 -31.7 -75.4 68.4

850 ºC 30 134.2 179.2 138.9 76.9 40.3

As cast

HT: 300 ºC/1 day

HT: 850 ºC/30 min

Heating

Exo

Cu-11.35Al-3.2Ni-3Mn-0.5ZrHeat/cooling rate:

20 K/min

Spray forming of Cu-based SMAs

Slide 23

SampleTensão

máxima (MPa)Yield Stress

(MPa)Deformação até

ruptura (%)

As-Cast 936.51 426.27 5.25

850°/30 min 912.38 383.14 7.52

300°/1 day 856.96 590.54 3.24

Roh et al. [2] 380 - 560 200 4.5 - 5.5

Morris et al. [12] 625 280-300 6 – 7

0

250

500

750

1000

0 1 2 3 4 5 6 7 8True Strain (%)

Tru

e S

tre

ss

(M

Pa

)

300 ºC/ 1 day 850ºC/30 min As Cast

Cu-11.35Al-3.2Ni-3Mn-0.5Zr

Spray forming of Cu-based SMAs

tensile tests

Slide 24

24

A strong influence on grain size, thermal stability and mechanical behaviour was observedwith small addition of Zr to a spray formed Cu-11.85Al-3.2Ni-3Mn (wt%) SMA.

The grain size decreases almost 5x, reaching sizes usually observed only afterthermomechanical processing.

The addition of Zr also changes the mechanical behaviour, increasing the tensile ductilityand improving the work-hardening behaviour. The fracture strength increases almost twotimes (at room temperature) when compared with the alloy without Zr.

The transformation temperatures of the Zr-added SMA are very sensitive to thermaltreatments.

By controlling the process parameters and carrying out post-treatments, the new Cu-Al-Ni-Mn-Zr alloy can be design to different applications.

Spray forming of Cu-based SMAs: conclusions

Slide 25

S. Pauly, Mater Today 2013

• Layer-by-layer process, small liquid volumes

• High intrinsic cooling rates metastable phases/microstructures

• Cu-11.85Al-3.2Ni-3Mn and Cu-11.35Al-3.2Ni-3Mn-0.5Zr

• Zr: grain refiner

• Relative density: 98.8 – 99.8%

• Suction casting (rapid quenching) for comparison

• Role of Zr on microstructure and SME?

• Effect of annealing?

• Effect of processing on SME?

Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

Slide 26

Cu-11.85Al-3.2Ni-3MnCu-11.35Al-3.2Ni-3Mn-0.5Zr

• β1’ is the main phase

• Unambiguous phase identification aggravated: broad peaks, multitude of phases

• Annealing treatment: 850 °C for 10 min (water quench) + 300 °C for 60 min (cooling in air)

• After annealing: β1, α(?) and γ1’(?) and additional phase

EDX

EBSD

Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

T. Gustmann, S. Pauly et. al. Shap. Mem. Superelasticity 2016

Slide 27

Cu-11.85Al-3.2Ni-3Mn (cast, centre) Cu-11.35Al-3.2Ni-3Mn-0.5Zr (cast, centre)

Cu-11.85Al-3.2Ni-3Mn (SLM) Cu-11.35Al-3.2Ni-3Mn-0.5Zr (SLM)

27Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

T. Gustmann, S. Pauly et. al. Shap. Mem. Superelasticity 2016

Slide 28

Cu-11.4Al-2.5Ni-5Mn-0.4Ti

• Cu2ZrTi (X phase) in Cu-Al-Ni-Mn-Ti

• Cu2AlZr (Y phase, isomorphous to the X phase)

• Y phase very fine in as-prepared state

• Y phase coarsens after annealing can be identified by EBSD

• No hints of α, γ2 or NiAl

• Effect of Y phase during annealing?

4 µm

28

J. Dutkiewicz, MSEA 1999

cast Cu-11.35Al-3.2Ni-3Mn-0.5Zr, annealed

Cu2AlZrβ1‘

Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

T. Gustmann, S. Pauly et. al. Shap. Mem. Superelasticity 2016

Slide 29

• Transformation temperatures with Zr additions

• No compositional gradients across the samples

• Fine Y phase: jerky transformation

• Fine Y phase: increase in MT temperatures

• Zr segregates at the boundaries when cooling rate

• Annealing: coarse Y phase at grain boundaries

no more MT

29

T. Tadaki in Shape memory materials, 1998

Cu-11.35Al-3.2Ni-3Mn-0.5Zr

Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

T. Gustmann, S. Pauly et. al. Shap. Mem. Superelasticity 2016

Slide 30

• Typical double yielding

• Significant plastic strain in compression

• SLM comparable to casting

• Ductility of SLM samples exceeds that of cast samples

• Annealing increases strength and reduces ductility

presence of coarse Y phase

30

compression tension

Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM

Slide 31

SLM produces refined grains

Zr leads to precipitation of Y phase (Cu2AlZr)

Very fine Y phase during SLM (also inside grains)

Segregation of Zr at grain boundaries (cooling rate dependent)

preferential formation of Y phase during annealing

pinning of interfaces (grain refinement)

SLM samples: mechanical properties comparable to cast samples

Pseudoelasticity significantly reduced when Y phase is present

Coarse Y phase better recovery

Energy dissipated during SLM , transformation temperatures

Via SLM, the transformation properties can be adjusted

No need for additional thermo-mechanical post-treatments

31Phase formation, thermal stability and mechanical properties of Cu-based SMA produced by SLM: conclusions

Slide 32

Thank you for your attention!

Piter Gargarella

piter@ufscar.br