Stage I – Several demonstration components were SLM fabricated using the EOS system with Magics supports in order to assess the feasibility of the process to produce particular
3.15. Mechanical Testing
The mechanical validation of the SLM processing route was via tensile and creep testing. Bars were built 12 mm diameter and 65 mm long (except where material was limited) using
‘pin-style’ supports. Bars were built both longitudinally and transversely to the build direction (Z-axis) to study the influence of build orientation on mechanical properties.
Following fabrication the bars were subject to different HIP and heat treatments conditions (see Table 3.5 & Table 3.6) before being machined to the appropriate test-sample geometry.
110 i. Tensile Testing
All tensile testing was carried out in accordance with the ASTM standard (E8/E8M-09 [23]).
CM247LC room temperature tensile testing was carried out in the mechanical testing lab (Met. & Mat. UoB); elevated temperature tensile testing and creep testing was carried out externally by Incotest UK. Tensile samples were machined to standard M8 threaded cylindrical test pieces, 4 mm, test section as shown in Figure 3.12
Figure 3.12: Dimensioned drawing of M8 threaded tensile test bar used for room temperature and elevated temperature tensile tests.
All tensile testing was carried out using a physically connected extensometer and the constant crosshead speed method. Crosshead speed was set at 0.35 mm/min to determine yield (upto 0.2% proof stress). This value was determined in accordance with section 7.6.3.3 of the ASTM standard which states that the crosshead speed should be set to 0.015 0.003 mm/mm/min of the original reduced section length (23 mm for the M8 threaded test bar) [23].
Following 0.2% proof stress, the crosshead speed in the elevated temperature tensile tests was increased to 1.5 mm/min in accordance with section 7.6.4 of the ASTM standard [23] which states that to determine tensile strength, the crosshead speed should be set to between 0.05 and 0.5 mm/mm/min of the original reduced section length. Room temperature tests were allowed to continue at 0.35 mm/min until failure.
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For each test point, 3 samples following a similar processing route were tested. Room temperature tests were carried out with the aim of demonstrating the differences in build orientation and the application of the HIP treatment whereas the elevated temperature tests were all carried out using vertical test bars with the same process route. IN625 samples were all tested in the as-fabricated condition. Table 3.9 lists the test conditions and the process route for the CM247LC bars, Table 3.10 lists the test conditions and process route for the CMSX486 bars and Table 3.11 lists the test conditions and process route for the IN625 bars.
Table 3.9: Tensile testing conditions for SLM fabricated CM247LC samples.
Temperature Process Route Build
Orientation No. of Samples Test Location
Room Temp. HT1 Vertical 3 UoB
1. SLM fabricated and Heat Treated (1260C, 2h, GQ; 980C, 5h, AC; 870C, 20h, AC)
2. SLM fabricated, HIPed (1180C, 150 MPa, 4h) and Heat Treated (1260C, 2h, GQ; 980C, 5h, AC;
870C, 20h, AC)
Table 3.10: Tensile testing conditions for SLM fabricated CMSX486 samples.
Temperature Process Route Build
Orientation No. of Samples Test Location
Room Temp. HT1 Vertical 3 Incotest
Room Temp. HT1 Horizontal 3 Incotest
1. SLM fabricated and Heat Treated (1318C, 2h (see HT section), GQ; 1140C, 6h, AC; 871C, 20h, AC)
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Table 3.11: Tensile testing conditions for SLM fabricated IN625 samples.
Temperature Process Route Build
Orientation No. of Samples Test Location
Room Temp. As- Fabricated Vertical 3 Incotest
Room Temp. As- Fabricated Horizontal 3 Incotest
540C As- Fabricated Vertical 3 Incotest
540C As- Fabricated Horizontal 3 Incotest
760C As- Fabricated Vertical 3 Incotest
760C As- Fabricated Horizontal 3 Incotest
ii. Creep Testing
High temperature creep testing was carried out at Incotest UK in order to establish the effect of the process route and the overall high temperature creep performance of the SLM fabricated material via this process route. 2 samples were tested under each condition for CM247LC and CMSX486, creep testing was in accordance with BS EN 2002-005:2007 [24].
Creep specimens were machined to standard 14G specification with 4 mm test section as shown in Figure 3.13.
Figure 3.13: Dimensioned drawing showing 14G creep specimen.
All creep tests were carried out at 1050C, 100 MPa; Table 3.12 and Table 3.13 list specimen conditions for CM247LC and CMSX486 samples respectively.
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Table 3.12: Creep test conditions for CM247LC specimens.
Temperature/Stress Process Route Build
Orientation No. of Samples Test Location
1050C/100 MPa HT1 Vertical 2 Incotest
1050C/100 MPa HT1 Horizontal 2 Incotest
1050C/100 MPa HIP & HT2 Vertical 2 Incotest
1050C/100 MPa HIP & HT2 Horizontal 2 Incotest
1. SLM fabricated and Heat Treated (1260C, 2h, GQ; 980C, 5h, AC; 870C, 20h, AC)
2. SLM fabricated, HIPed (1180C, 150 MPa, 4h) and Heat Treated (1260C, 2h, GQ; 980C, 5h, AC;
870C, 20h, AC)
Table 3.13: Creep test conditions for CMSX486 specimens.
Temperature/Stress Process Route Build
Orientation No. of Samples Test Location
1050C/100 MPa HT1 Vertical 2 Incotest
1050C/100 MPa HT1 Horizontal 2 Incotest
1. SLM fabricated and Heat Treated (1318C, 2h (see HT section), GQ; 1140C, 6h, AC; 871C, 20h, AC)
3.16. Summary
This chapter has presented the key experimental techniques used in the generation of the results presented and discussed in the following chapters. The practical application of the SLM process is further outlined in appendix A and a summary of the central composite design of experiments methodology employed for the parametric studies of CMSX486 and IN625 is presented in Appendix B.
114 3.17. References
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