developed material were investigated by applying wear and creep tests. Certain area in the microstructure have been analysed
with SEM.
8.2 Experimental Conditions
In the frame of the present work, pure thin sheet nickel and titanium were chosen, for the facility of the joining operation, a
pure aluminium foil was also used. All of the specimens were prepared from different size of scrap sheets by water jet cutting
in the Supmeca-Paris, research laboratory. As the reinforcements very fine niobium and TiB 2 powders were used to improve
mechanical performance of the composites. All of the specimens were first brushed very rough SiC papers then cleaned with
acetone in order to remove any dirty particles at the surfaces before hot forging process.
All of the sheets were stacked on the top each other in a special steel die then pressed. After that, it has put in the electrical
oven and waited under argon atmosphere up to the hot forging process. After homogenous heating, the composite was forged
at 600–650
C by a hydraulic press at the level of 300–350 MPa rolled just after being taken out of the furnace. At the second
stage of this process, a post heat treatment was carried out.
For the sake of the simplicity, sintered and sintered-forging specimens were compared by means of low velocity impact
(drop weight) tests carried out with a drop tower. The response of theses composites were evaluated under the dynamic
loading conditions.
Three-point bending tests were carried out on tests were carried out with a Zwick mechanical test system at the strain rate of
1 mm/min.
Wear tests were carried out by using the scratch capability of a nanoindenter. A normal load 50mN was applied over a
linear wear track of 500 and 1000 μm for 50 cycles. One cycle is defined as a pass and return over the track. A conical tip with
a 90
cone angle was used for these tests. The speed of the tip during wear tests was 50 μm/s. A total of 10 wear tests were
performed for each sample. Again, creep test were performed with the nanoindenter to evaluate the time dependent response
of the manufactured composites. On each sample 25 indents were performed on a 5 Â 5 grid with a Berkovich indenter. The
indents were spaced 50 and 75 μm along the sides of the grid. The load was increased at a rate of 5 mN/s to the max load of
50 mN and kept at the load for 500 s then unloaded. Modulus and nano hardness measured calculated during the unload stage
of the creep test.
With the finite element model developed with reference to these tests, the mechanical behaviour of the material is
supported by simulations made with the Abaqus software in order to compare with certain experimental results. The
microstructure of the defined areas on the specimens have been analysed with SEM.
8.3 Results and Discussion
8.3.1 Microstructure and Mapping Analyses of the Compositions
Figure 8.1 show a typical microstructure of the sandwich sheet specimen TiNi based composites and also EDS chemical
analyse taken on the SEM with back scattered option (BES). A homogenous a sound microstructure is observed with very fine
diffusion due to hot bonding process that hot forging was performed at 650
C under the inert atmosphere.
As indicated just before, Mapping analyses give a safety observation on the composite structure. Here, distribution of the
reinforcements as very fine particles and position of the stacked layer (thin sheets and diffusion of the fine particles inside of
these layers can be perceived by means of “Mapping” analysis as indicated in the Fig. 8.2.
That is reason we suggest this process called hot forging bonding process especially for the recycled scrap sheets as a low
cost, alternative and more advantageous manufacturing process to design the composite sheets.
8.3.2 Mechanical Behaviour-Superelasticity: 3-Point Bending Test Results
Elasticity behaviour and damage analyses of the TiNi sandwich composite sheets have been evaluated by using 3P-Bending
tests under quasi static test conditions. All of the experimental tests was carried out according to the ASTM 790. Standard test
specimens were prepared from hot forged layered composite. Figure 8.3 present all of the set up installed on the Zwick
54
H. M. Enginsoy et al.
with SEM.
8.2 Experimental Conditions
In the frame of the present work, pure thin sheet nickel and titanium were chosen, for the facility of the joining operation, a
pure aluminium foil was also used. All of the specimens were prepared from different size of scrap sheets by water jet cutting
in the Supmeca-Paris, research laboratory. As the reinforcements very fine niobium and TiB 2 powders were used to improve
mechanical performance of the composites. All of the specimens were first brushed very rough SiC papers then cleaned with
acetone in order to remove any dirty particles at the surfaces before hot forging process.
All of the sheets were stacked on the top each other in a special steel die then pressed. After that, it has put in the electrical
oven and waited under argon atmosphere up to the hot forging process. After homogenous heating, the composite was forged
at 600–650
C by a hydraulic press at the level of 300–350 MPa rolled just after being taken out of the furnace. At the second
stage of this process, a post heat treatment was carried out.
For the sake of the simplicity, sintered and sintered-forging specimens were compared by means of low velocity impact
(drop weight) tests carried out with a drop tower. The response of theses composites were evaluated under the dynamic
loading conditions.
Three-point bending tests were carried out on tests were carried out with a Zwick mechanical test system at the strain rate of
1 mm/min.
Wear tests were carried out by using the scratch capability of a nanoindenter. A normal load 50mN was applied over a
linear wear track of 500 and 1000 μm for 50 cycles. One cycle is defined as a pass and return over the track. A conical tip with
a 90
cone angle was used for these tests. The speed of the tip during wear tests was 50 μm/s. A total of 10 wear tests were
performed for each sample. Again, creep test were performed with the nanoindenter to evaluate the time dependent response
of the manufactured composites. On each sample 25 indents were performed on a 5 Â 5 grid with a Berkovich indenter. The
indents were spaced 50 and 75 μm along the sides of the grid. The load was increased at a rate of 5 mN/s to the max load of
50 mN and kept at the load for 500 s then unloaded. Modulus and nano hardness measured calculated during the unload stage
of the creep test.
With the finite element model developed with reference to these tests, the mechanical behaviour of the material is
supported by simulations made with the Abaqus software in order to compare with certain experimental results. The
microstructure of the defined areas on the specimens have been analysed with SEM.
8.3 Results and Discussion
8.3.1 Microstructure and Mapping Analyses of the Compositions
Figure 8.1 show a typical microstructure of the sandwich sheet specimen TiNi based composites and also EDS chemical
analyse taken on the SEM with back scattered option (BES). A homogenous a sound microstructure is observed with very fine
diffusion due to hot bonding process that hot forging was performed at 650
C under the inert atmosphere.
As indicated just before, Mapping analyses give a safety observation on the composite structure. Here, distribution of the
reinforcements as very fine particles and position of the stacked layer (thin sheets and diffusion of the fine particles inside of
these layers can be perceived by means of “Mapping” analysis as indicated in the Fig. 8.2.
That is reason we suggest this process called hot forging bonding process especially for the recycled scrap sheets as a low
cost, alternative and more advantageous manufacturing process to design the composite sheets.
8.3.2 Mechanical Behaviour-Superelasticity: 3-Point Bending Test Results
Elasticity behaviour and damage analyses of the TiNi sandwich composite sheets have been evaluated by using 3P-Bending
tests under quasi static test conditions. All of the experimental tests was carried out according to the ASTM 790. Standard test
specimens were prepared from hot forged layered composite. Figure 8.3 present all of the set up installed on the Zwick
54
H. M. Enginsoy et al.