production advantages using laser cladding as an … · production advantages using laser cladding...
TRANSCRIPT
Production advantages using laser cladding as an additive manufacturing method
ObjectiveIs it possible to obtain the same material characteristics of a component using laser cladding as an additive manufacturing method compared to producing the component conventionally?
This poster describes industrial trials with laser cladding and precipitation hardening heat treatment of thinwalled structures with the 17-4 PH stainless steel alloy. Due to the great relevance of the AM production methods for the aviation industry, the mechanical strength of the alloy given by the MMPDS document is used as a baseline. In order to improve the properties of the produced specimens, hot isostatic pressing was applied
Conclusion and Outlook• The fabricated AM 17-4 PH responds
readily to conventional H900 and H1100 heat treatments.
• Poor elongation caused by a porous initial microstructure can be improved by a HIP treatment.
• With the HIP treatment, the AM 17-4 PH complies with MMPDS minimum mechanical strength and elongation values.
It would be highly relevant for the applica-tion of 17-4 PH to the aviation industry to verify whether the fatigue strength pro-perties are also comparable to those of conventionally produced 17-4 PH.
Uffe Ditlev Bihlet, Michel Honoré and Peter Tommy Nielsen
Method and TestsThe AM 17-4 PH samples are manufactured using a purpose-built and commercially available laser cladding system. The powder entering the laser focal point is melted and deposited on the sample surface. Laser powers in the range 1.4 kW to 2.1 kW were applied. Hereafter the items are heat treated as per scheme Table 1.
Hot Isostatic Pressing (HIP) is a common post-treatment which is routinely used on cast turbine components and on powder metallurgical parts. This treatment causes a signifi-cant improvement of the mechanical properties by closing and diffusion bonding internal pores and defects. This is accomplished at a high external pressure in the range of 800-1000 bar and at temperatures close to the melting point of the alloy.
The mechanical properties were quantified by tensile testing and elongation. The tensile test was conducted as described by ISO EN 6892-1. Samples were oriented in the build direction as well as perpendicular to the build direction. The fracture surfaces were inspected using scanning electron microscopy.
Table 1. Heat treatments.
Treatment HIP Solution treatment Ageing
As fabricated - - -
H900 - 1030°C x ½ hour 482°C x 1 hour
HIP+H900 X 1030°C x ½ hour 482°C x 1 hour
HIP+H1100 X 1030°C x ½ hour 593°C x 4 hours
Minimum value as defined by MMPDS-08
744 721
1291
1406
1190
10181060
1361
1560
1240
500
700
900
1100
1300
1500
1700
1900
As fabricated As fabricated -Z-direction
H900 -Z-direction
HIP+H900 HIP+H1100
MP
a
0.2 % yield stress Ultimate tensile strength
7,7
5,8
3,4
13,2
14,1
0
2
4
6
8
10
12
14
16
% e
long
atio
n
Minimum value as defined by MMPDS -08
As fabricated As fabricated -Z-direction
H900 -Z-direction
HIP+H900 HIP+H1100
Electron microscopy image of fracture surface
Microstructure of AM 17-4 PH before and after the HIP treatment
As fabricated
Porosity
Closed porosity
HIP+H900
ResultsThe results show that a post processing treatment consisting of a HIP cycle and a conven-tional precipitation hardening, vastly improves the mechanical strength and elongation va-lues of printed specimens, causing them to exceed the specified MMPDS values.
forcetechnology.com