JBK-75 is an iron-nickel derivative alloy of A-286 that has been of interest to NASAs propulsion community for use in fuel injectors and other components that are used in hot, corrosive environments. To enable the rapid production of these components in JBK-75, Marshall Space Flight Center has developed parameters for manufacturing fully dense JBK-75 components using powder bed fusion additive manufacturing (PBFAM). These parameters were developed in a two-step development. First, the depth of laser penetration in the powdered material was measured across a spectrum of laser powers to determine the optimal power necessary for generating the desired meltpool depth. The parameter sets vector-to-vector spacing was then then tailored to guarantee the full densification of the desired area. The results of this development was a readily implementable parameter that produced 99.6% dense material when using a 147W power running at 600mm/s with a 85m(32%) vector-to-vector spacing

Gradl, P. R.

Jones, Z. C.

English

NASA Technical Reports Server

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
POWDER BED FUSION ADDITIVE MANUFACTURING OF JBK-75 
 
Z.C. Jones, P.R. Gradl 
National Aeronautics and Space Administration 
Marshall Space Flight Center  
Huntsville, Alabama 
https://ntrs.nasa.gov/search.jsp?R=20200000999 2020-03-28T19:07:11+00:00Z
ABSTRACT 
JBK-75 is an iron-nickel derivative alloy of A-286 that has been of interest to NASA’s 
propulsion community for use in fuel injectors and other components that are used in hot, 
corrosive environments. To enable the rapid production of these components in JBK-75, Marshall 
Space Flight Center has developed parameters for manufacturing fully dense JBK-75 
components using powder bed fusion additive manufacturing (PBFAM). These parameters were 
developed in a two-step development. First, the depth of laser penetration in the powdered 
material was measured across a spectrum of laser powers to determine the optimal power 
necessary for generating the desired meltpool depth. The parameter set’s vector-to-vector 
spacing was then then tailored to guarantee the full densification of the desired area. The results 
of this development was a readily implementable parameter that produced 99.6% dense material 
when using a 147W power running at 600mm/s with a 85µm(32%) vector-to-vector spacing.  
INTRODUCTION 
JBK-75 was first developed as a derivative alloy of A-286 that improved upon its 
predecessor’s weldability as well as its hydrogen compatibility for use in applications that called 
for a precipitation hardened steel with high strength up to 922K (1,200°F) in both air and 
hydrogen. [1] As early as 1993, NASA began identifying JBK-75 as an alloy of interest in nozzles 
and fuel injectors. Drawbacks emerged in the implementation of JBK-75 in complex components, 
however, particularly in regards to machining it. The material’s extreme abrasiveness resulted in 
a low tool life and a trade-off between chip control and surface finish [2], and thus an expensive 
and time-consuming machining operation. 
In an effort to reduce the lead time and cost of JBK-75 parts, Marshall Space Flight 
Center (MSFC) began a project in 2018 to develop an additive manufacturing process for the 
alloy using a powder bed fusion process. The goal of the project was to prove the additive 
manufacturability of JBK-75 and produce a parameter set for PBFAM machines that allow for the 
production of fully dense components that require minimal machining or post processing. 
Parameter sets are intrinsically necessary for an additive manufacturing process as 
contain the data that the machines use to coordinate the interdependent laser, focusing, and 
powder deliver systems that comprise the core of the platforms. Each alloy must have a 
parameter set developed for it, which is done by producing groups of samples made with different 
combinations of laser power, speed, and vector-to-vector spacing, also known as the hatch 
spacing, that together control the total energy input into the powder bed and thus how the powder 
is melted. [3] These samples are then cut and polished and analyzed either for the depth of the 
laser penetration or the density of the bulk material, at which point only parameters that produce 
the highest density continue to be developed by testing and verifying mechanical and 
microstructural properties. 
It is a rarity for a single parameter set to be the one and only parameter set that a 
material can be run at. Instead, there is often a range of parameters within which a material can 
be successfully produced and which may allow you to prioritize certain elements of the production 
over others, i.e. a better surface finish may be achieved by running the laser slower, albeit at a 
cost of the component taking longer. [4] NASA’s position in regards to this is to prioritize the 
density of the final part as the critical element of a parameter set with the speed of production 
being a secondary concern.  
JBK-75 is primarily iron, nickel, and chromium with minor amounts of aluminum, titanium, 
and molybdenum and a melting point of 1672K (2.500°F). [5] The composition and melting point 
is most similar to Inconel 718 alloy that MSFC has extensive experience additively manufacturing 
and analyzing, and so the initial starting points for the development were based on the current 
parameter set for Inconel 718, which runs at 180W, 600mm/s, and a hatch spacing of 105µm.  
RESULTS AND DISCUSSION 
EXPERIMENTAL 
  A ConceptLaser M1 PBFAM 
machine was used to manufacture the 
samples used in this project. This machine 
was chosen because it allowed for the 
complete editing of the parameters. There 
was a working familiarity with each 
parameter as well after having been 
extensively manipulated in previous 
developments of other alloys. The M1 had 
also been used exhaustively in the 
development of the Inconel 718 parameters 
that were used as the starting point, and 
so the machine and its idiosyncrasies 
were well known to the operators and engineering staff. 
 The recoating system for the M1 was fitted with a stainless steel blade for this 
development due to the need for strict control of the powder layer thickness to ensure that the 
later analysis for melt-pool penetration and density were correct and not subject to layer thickness 
variations. [6] The steel blade also eliminates the possibility for a test sample to warp upward and 
damage the recoater blade and cause a defect across the Y axis of a build, potentially causing a 
whole row of samples to be lost. Instead, should a test specimen fail in that manner the recoater 
blade will hit the sample, the torque limit on the recoating mechanism will be trigger, and the build 
will be paused and allow for the operator to cancel and remove the failing sample but continue 
with the remaining samples.  
 The sample geometry used in this project is a straightforward 25 x 10 x 19mm cube with 
0.5mm fillets on the Z-axis edge and base cone that 
slopes at a 60° angle up to the full area. Cone bases 
are frequently used within NASA’s AM lab to allow for 
test samples to be pulled off the build plate with pliers 
rather than having to be machined off, saving 
development time for the samples as well as reducing 
mundane machining operations to a minimum. The 
build plate itself was a standard 316L stainless steel 
build platen. 
 Fifty-four total samples were initially produced 
in this development, with the samples being varied in 
both power and the hatch spacing but having a locked 
laser speed of 600mm/s. The layout and the labels 
are given in detail in figure 3. The variation in both 
hatch spacing and power allowed for the samples to 
serve both development goals simultaneously and 
reduce the number of sample cuts required. The 
samples at the highest range of vector-to-vector 
spacing could be used to measure the meltpool depth, 
which would then guide which power samples were 
analyzed, allowing for a very rapid development that required only 14 of the total samples to be 
sectioned. 
The depth of the melt-pool is a critical element in a usable parameter set and a function of the 
Concept Laser M1 
Version 2012 Model (Gen 1) 
Build Capacity 250mm x 250mm x 275mm 
Laser Single 400W Nd:YAG 
Spot Size 52µm 
Laser travel 
Speed 
50-5,000 mm/2 
Inert Gas Argon 
Ventilator Flow 41% 
Figure 1: ConceptLaser M1 Specifications 
Figure 2: Sample geometry 
energy being put into the material by the laser. If the energy input in insufficient, the resultant 
melt-pool will be too shallow, fail to connect with the previous layers, and thus produce a defect-
riddled part at best. [7] On the other hand, if the energy input is too high then the melt-pool will 
elongate, over penetrate into the previous layers, and form a deep melt-pool disrupted by the 
collapse of metal vapor pockets. The melt-pool then solidifies before it has the opportunity to 
stabilize and porosity is left by the perturbations. [8] The results of both these extremes is the 
same - a part with defects and porosity throughout the structure. For stainless steels and similar 
alloys, NASA’s parameter sets target 2-4 layers of penetration, roughly 120-160µm from the top 
of the powder surface.  
Once the power level needed to generate the ideal melt-pool depth is determined, the next 
element to determine is the hatch spacing. Hatch spacing is the distance between each pass of 
the laser as it rasterizes the part layer. Should the hatch spacing be too wide, the part will have 
visible gaps between each pass of the laser, resulting in a highly porous, low density part. 
Opposite of that, if the hatch spacing should be too close together then the vectors will overlap 
too much and the part will see too much heat input and develop the aforementioned turbulent 
melt-pool. While the exact hatch spacing is highly materially dependent, stainless steels have 
normally shown an optimal hatch spacing is in the range of 20- 40% of the melt-pool radius 
overlapping into the previous vector. [3] 
 
 Samples were analyzed by first being cut by a cooled sectioning saw, hot mounted and 
polished. If the samples are being analyzed for melt-pool depth, they are then etched to reveal 
the individual melt-pools. If the samples are only being analyzed for hatch spacing then etching is 
not required as the hatch spacing will become evident in the porosity or lack thereof in the part. 
Power (W) 
147 
155 
163 
171 
181 
190 
 
Hatch Spacing  
(Label value - µm) 
70 - 105 µm 
67 - 100 µm 
63 - 95 µm 
60 - 90 µm 
57 - 85 µm 
54 - 81 µm 
51 - 76 µm 
49 - 73 µm 
46 - 70 µm 
Figure 3: Sample build 
layout. Gas flow and 
recoating direction are 
denoted by the black 
arrow. Power level and 
hatch-spacing included in 
the tables to the left. 
The exact density of the part is then analyzed using threshold image analysis provided by the 
ImageJ2 program. 
RESULTS 
 The samples at 105µm spacing were first cut and analyzed for melt-pool depth. It was 
immediately evident that the melt-pools were much deeper than anticipated. The range of depths 
seen was between 155um to 240um, whereas in Inconel 718 the comparable parameters would 
be generating depths that were half of that.  
   
   
Figure 4: Etched samples and average calculated depths. 
As can be seen in the pictures, the melt-pools are extremely deep and elongated in the at 
171W, but decrease down to an acceptable 155um at 147W. While 155W is also in an acceptable 
range, 147 was ultimately the one that was chosen. At 147W the depths were more tightly 
grouped around 155 +- 15um as well as being more consistently ~125um in surface diameter. 
Minimal elongation of the melt-pool was also seen at 147W, whereas 155 showed irregular 
elongation. These features combined created a highly predictable melt-pool that could be easily 
adjusted with hatch spacing to create a fully dense part.  
 The 147W power samples were then analyzed for density to determine the hatch spacing 
that provided the most fully dense bulk material. Most of the samples; density stayed well above 
99.2%, although an ejecta-interference issue was discovered and will be discussed in the next 
section. The highest density was found at 147W – 85µm at 99.6%. This corresponds to a 32% 
overlap between the vectors.  
Sample (Power(W) – Hatch Spacing(µm)) Density 
147 - 100 99.33% 
147 - 95 97.91 *See next section on Ejecta Control. 
147 - 90 99.45% 
147 - 85 99.68% 
147 - 81 93.95% *See next section on Ejecta Control. 
147 - 76 99.65% 
147 - 73 99.62% 
147 - 70 89.78 *See next section on Ejecta Control. 
Figure 5: Densities of the 147W hatch spacing samples. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 6: Sample 147-85 optical microscopy and image 
threshold to determine the density of the bulk material. 
The porosity that was found was finely distributed across the part and did not congregate 
into specific areas or follow particular patterns. The average size of the pores was below <20µm 
with no pores being found to contain loose powder or partially sintered material to indicate that a 
lack of fusion occurred. With the fully dense part well beyond the minimum density required to 
produce usable material, the parameters listed in figure 7 have been accepted as workable JBK 
parameters. 
JBK-75 Parameter Set 
Power Speed Hatch Spacing 
147 W 600 mm/s 85um 
Figure 7: Final core parameters for JBK-75 
EJECTA CONTROL 
 JBK-75 alloy produced significant amounts of ejecta during the build process, a well-
known and documented phenomenon in the additive manufacturing process. The exact cause for 
this ejecta is a topic of debate and beyond the scope of this paper, however several samples of 
the JBK-75 showed massive degrees of porosity if they were directly in the ejecta path of a large 
number of parts. The current theory for why this porosity develops is that the misshapen ejecta 
particles cause small scale disruptions to the powder layering. As the powder layers are 
disrupted, the melt-pool becomes unstable and no longer fully fuses the powder, resulting in 
porosity. [9] The exact amount of ejecta falling onto a part to cause significant porosity is not yet 
know, but a mitigating laser scanning strategy was developed by MSFC. The strategy uses the 
laser to do a secondary, low power laser pass once all parts in a layer have been done to remove 
or melt accumulated ejecta from the exposed surface and allows for the fresh powder to 
successfully layer onto the part.   
   
Figure 8: Sample 147-95 without 
cleaning pass (Left) and with 
cleaning pass (right). 
 
 
 
 
 
 
 
 
 
 
 
 
Parameter 
Set 
Without Cleaning 
Pass  
With Cleaning 
Pass 
147 - 95 97.91% 99.41% 
147 - 81 93.95% 99.23% 
147 - 70 89.78% 99.08% 
Pass Parameters 
Power 150W 
Speed 2000mm/s 
Hatch 
Spacing  
105µm 
SUMMARY AND CONCLUSIONS 
JBK-75 has proven to be a readily usable alloy in PBFAM machines. Over the course of 
the development it has been shown to sustain a stable melt-pool as well as achieve an 
acceptable density of 99.6% across the bulk material without any secondary steps or processes 
being taken to further consolidate the material. In the event that significant ejecta should be noted 
in the build process, a prudent step to take at the current time is to implement the laser cleaning 
pass to clear the build surface of ejecta, however it is still highly recommended to take metallurgy 
samples and evaluate the density of the material in any build that sees significant ejecta.  
 
FUTURE WORK 
JBK-75 is an ongoing development process at MSFC and upcoming tasks include but are 
not limited to mechanical testing, the development of contour and support material parameters, 
verifying that traditional JBK-75 heat treatments are equally successful with additively 
manufactured JBK-75, and further investigation of the powder-ejecta interactions. MSFC will also 
soon begin the development of HR-1 alloy, a NASA developed derivative alloy of JBK that 
surpasses its predecessor in hydrogen compatibility.  
ACKNOWLEDGEMENTS 
Thank you to all the NASA personnel and contractors that worked on this project, in 
particular Ken Cooper, Paul Gradl, Ian Hanson, Colton Katsarelis, and Megan le Corre.   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Powder Bed Fusion Additive Manufacturing of JBK-75

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