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1 9

A D V A N C E D

M A T E R I A L S

&

P R O C E S S E S | J A N U A R Y

2 0 1 6

T

he Orion Multipurpose Crew Ve-

hicle is NASA’s vehicle for hu-

man exploration of deep space.

Its maiden voyage—Exploration Flight

Test 1—was an unmanned flight de-

signed to test the vehicle’s main sys-

tems, which launched from Kennedy

Space Center on December 5, 2014. The

trip included two earth orbits followed

by reentry at approximately 20,000mph,

subjecting the heat shield to 4000°F.

Landing and recovery took place in the

Pacific Ocean. Among the technology

advancements included on Orion were

additively manufactured (AM) vents

used as air passages for the unpressur-

ized portions of the spacecraft.

Exploration Flight Test 1 used four

vent assemblies to equalize pressure

between the unpressurized portions of

the spacecraft and the external environ-

ment. The assemblies contained the AM

housings and integral screens as well as

two additional screens that were weld-

ed on. Each assembly was then bolted

into the vehicle using three mounting

flanges. Complete assemblies were

roughly the size of a 1-liter water bottle.

Initial design called for a wire

mesh to be welded into the housing.

Multiple screens were needed for re-

dundancy, and a cylindrical shape was

desired due to space limitations inside

the vehicle. Because this initial design

proved difficult to produce, additive

manufacturing was proposed.

PARTS MANUFACTURING

Parts were additively manufac-

tured from a nickel alloy (Inconel 718)

using the vendor’s recommended pro-

cedure. (Note that this was before in-

dustry specification ASTM F3055 was

available for use.) Each build cycle con-

tained one part and corresponding test

coupons. Parts were additively manu-

factured, stress relieved, hot isostati-

cally pressed (HIP’d), solution treated,

and aged. This corresponds with ASTM

F3055, Class D, although the processing

parameters were not identical. Machin-

ing was performed on some surfaces

to remove the support structure or to

provide a smooth surface for fastener

installation. Welding was performed

using industry specification AWS D17.1.

Fig. 1 —

Complete passive vent

assembly. The mesh on the top

was welded onto the additively

manufactured housing.

Fig. 2 —

Close-up of passive vent, showing

AM screen details.

Fig. 3 —

Representative tensile specimens

after testing.

Development welds were performed

and examined to determine sufficiency

of the weld schedules.

DEVELOPMENT TESTING

Three witness coupons were print-

ed with each part, comprising tensile

specimens in the

x, y,

and

z

orientations

(where

x

and

y

are on the build plane

and

z

is in the build direction). Speci-

mens were manufactured as cylinders,

machined to a 0.25-in. test diameter,

and tested per ASTM E8 at room tem-

perature. All specimens met ASTM

F3055 Class D requirements and were

within 15% of specification values. Fig-

ure 3 shows typical specimens.

Three tensile specimens were in-

tentionally not HIP’d for comparison.

These non-HIP’d specimens exhibited

approximately the same strength as the

HIP’d specimens, suggesting that the

HIP process may not provide a signifi-

cant strength benefit.

Microstructural evaluations were

also performed. Overall, specimens ex-

hibited very little porosity. Grains were

finer near the edges than in the center

of the coupons. Specimens were free of

Laves phase, an undesirable interglob-

ular phase

[1,2]

. A typical microstructure

is shown in Fig. 4 (50

×

magnification).