Microstructures and mechanical behavior of Inconel 718 fabricated by selective laser melting

The microstructure of Additive Manufactured (AM) Inconel 718 in general and Selective Laser Melting (SLM), in particular is different from the material produced by conventional methods due to the rapid solidification process associated with the former. As a result, the widely adapted standard solution heat treatment temperature (

Microstructure and hardness studies of Inconel 718 manufactured by selective laser melting before and after solution heat treatment

Objective This paper provides a brief review of relatively new additive manufacturing technologies for the fabrication of unusual and complex metal and alloy products by laser and electron beam melting. A number of process features and product microstructures are illustrated utilizing 3D optical and transmission electron microscope image compositions representing examples of 3D materials science. Methods Processing methods involving electron beam melting (EBM) and a process referred to as direct metal laser sintering (DMLS), often called selective laser melting (SLM) are described along with the use of light (optical) microscopy (OM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) to elucidate microstructural phenomena. Results Examples of EBM and SLM studies are presented in 3D image compositions. These include EBM of Ti-6Al-4V, Cu, Co-base superalloy and Inconel 625; and SLM of 17-4 PH stainless steel, Inconel 718 and Inconel 625. Conclusions 3D image compositions constituting 3D materials science provide effective visualization for directional solidification-related phenomena associated with the EBM and SLM fabrication of a range of metals and alloys, especially microstructures and microstructural architectures.

https://cyberleninka.org/article/n/753005.pdf

Fabrication of Metal and Alloy Components by Additive Manufacturing: Examples of 3D Materials Science

High temperature deformation of Inconel 718

The constituents of nickel-base superalloys have been classified into solid solution formers, precipitate formers, carbide formers and surface stabilizers. The characteristics of solutes which would make them most suitable in each category have been specified and appropriate alloying elements have been identified. Nickel-base superalloys are hardened primarily by the precipitation of Ni3X type compounds. The occurrence and crystallography of precipitation of various kinds of Ni3X type precipitates have been considered. The role of substitution by alloying elements on mismatch and stability of phases has been discussed. The free electron model and the Engel-Brewer model have been applied for evaluating the stabilities of precipitates, and the role of the alloying elements in determining the stabilities of external and internal surfaces such as grain boundaries have been briefly outlined.

The role of alloying elements in the design of nickel-base superalloys

The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.

Morphology of y’ and y” precipitates and thermal stability of inconel 718 type alloys

Influence of coherency strains on precipitate shape in a FeNiTa alloy

I n t e r m e t a l l i c compounds of AsB s t r u c t u r e s a r e l a r g e l y used in the s t r eng then ing of F e N i a l l oys and Ni b a s e a l l oys . Among the v a r i o u s AsB p h a s e s which can be f o r m e d in t hese s y s t e m s the cubic (L12) Y' phase and the b o d y c e n t e r e d t e t r a g o n a l (DO22) V" phase a r e m o s t f r equen t ly encoun te red . The c r y s t a l l o g r a p h i c c e l l s of t he se two s t r u c t u r e s a r e given in Fig . 1. These s t r u c t u r e s can be f o r m e d by s t ack ing iden t i ca l c l o s e packed o r d e r e d l a y e r s of c o m p o s i t i o n AsB. The l a y e r s a r e ana logous to the {111} p lanes of the fcc s t r u c t u r e . In LI~ and DOra p h a s e s , B a t o m s a r e l oca t ed at the c o r n e r s of e q u i l a t e r a l t r i a n g l e s and r e c t a n g l e s , r e s p e c t i ve ly . The influence of s e v e r a l v a r i a b l e s on the s t ack ing s e quence of AsB s t r u c t u r e s has been s tud ied and d i s c u s s e d b y v a r i o u s authors .*-4 In N i N b F e a l l oys , Quist et al* fQund tha t a luminum add i t ions p r o m o t e the f o r m a t i o n of the 7 ' phase , i n i t i a l l y t o g e t h e r with the 7" phase , but a t h ighe r a luminum concen t r a t i ons , the DO~2 phase d i s a p p e a r s . The au tho r s d i s c u s s e d the c r y s t a l l o g r a p h i c c h a r a c t e r i s t i c s and a l so the m a t r i x e l e c t r o n i c f a c t o r s which could p r o m o t e the f o r m a t i o n of e i t he r Y' and 7" phase . Sinha s,4 examined s e v e r a l b i n a r y and q u a s i b i n a r y s y s t e m s . He inves t i ga t ed the inf luence of the e l e c t r o n i c concen t r a t i on of the i n t e r m e t a l l i c compounds upon t h e i r s t r u c t u r e and concluded that a t e / a -~ 8.65, the o r d e r e d s t r u c t u r e of the c l o s e p a c k e d l a y e r s changes f r o m t r i a n g u l a r to r e c t a n g u l a r . The e / a r a t i o i s def ined by the a v e r a g e p e r a tom of the to ta l number of e l e c t r o n s ou ts ide the i n e r t gas she l l s . In the p r e s e n t work we s tud ied the p r e c i p i t a t i o n h a r d ening of F e N i C o T a a l l oys within which both 7 ' and 7" p h a s e s we re iden t i f i ed . The inf luence of the p r e c i p i t a te c o m p o s i t i o n on t h e i r o r d e r i n g ( t r i angu l a r o r r e c t angu la r ) was i nves t i ga t ed and the r e s u l t s a r e r e p o r t e d in th i s note. E x p e r i m e n t a l p r o c e d u r e s T h e compos i t i on of the a l l o y s i n v e s t i g a t e d i s g iven in Table I. The a l l o y s cont a ined a low ca rbon content ( 0.01 wt pet) . A Ta content of 3 a t . pe t was chosen. The Co/Ni r a t i o g r a d u a l l y i n c r e a s e d f r o m 0 to 0.71. Al loy 1 was p r e v i o u s l y s tudied , s'6 The e x p e r i m e n t a l p r o c e d u r e ~sed to p r e p a r e a l l oys 2, 6, and 7 was the s a m e as tha t d e s c r i b e d p r e v i o u s l y for a l l oy 1. The o the r a l l oys we re a r c m e l t e d under a p a r t i a l p r e s s u r e of a r g o n to g ive s m a l l ingots of about 20 g. Af te r ho t fo rg ing they we re homogen ized for 48 h at 1473 K in an a rgon a t m o s p h e r e . With the excep t ion of a l loy 7 the

R. Cozar

Papers

Morphology of y’ and y” precipitates and thermal stability of inconel 718 type alloys

Influence of coherency strains on precipitate shape in a FeNiTa alloy

Influence of the co/ni ratio on the γ and γ " precipitation in fe-ni-co-ta alloys

Durcissement par precipitation d'un alliage Fe - 30 % Ni - 9 % Ta