LDRD Final Report: Exploiting LENS Technology Through Novel Materials

Abstract

Laser Engineered Net Shaping (LENS) is a direct fabrication process in which metal powders are deposited into a laser melted pool, with succeeding layers being deposited to build up complex engineering shapes. This process is a rapid, low cost, low footprint, direct fabrication technique that lends itself to the concept for advanced manufacturing. It is especially suited for rapid prototyping and small lot production. However, previous work has developed LENS as an advanced manufacturing tool, rather than exploiting its potentially unique attributes. These attributes include: real time control of microstructure, tailored material properties at different locations in the same part, the production of graded thermal expansion parts, etc. In this program, the important metallurgical parameters, solidification velocity and cooling rate, have been characterized and process models developed that are being used as input to microstructural models. Residual stresses were measured and process maps developed for controlling residual stresses and melt pool size that are critical for controlling part dimensions and quality. Tool steels and two stainless steels have been used as model systems to demonstrate the concept and feasibility of utilizing the high solidification velocities and cooling rates to design microstructures and properties to meet functionality. It has also been shown that starting powder characteristics can greatly affect build quality, especially intralayer porosity. Limited work on ceramic materials indicates that novel material can be fabricated using this technology. This work has added a new dimension in designing and fabricating engineering components with novel microstructures and properties using this rapid prototyping technology.3

Laser rapid forming of SS316L/Rene88DT graded material

“…(2, 9 and 10), and the Ivantsov solution, the amount of constitutional undercooling ahead of the solidification interface and the growth velocity of equiaxed crystals can be determined. The maximum radius, r e , of the equiaxed crystal can be obtained by the following function: (14) where V e is the equiaxed crystal growth velocity, z n the distance from the solid/liquid interface in the liquid, where the undercooling is equal to the nucleation undercooling T n . Since the nucleation sites occur randomly, the actual volume fraction of equiaxed crystals is obtained by applying the Avarami equation [24],…”

“…They briefly studied the effects of rates of solidification on the mechanical properties of the graded materials. As for process development, Griffith et al [13,14] and Lewis and Schlienger [15] crostructural evolution in these alloys. Turning to non-ferrous materials, Pei and de Hosson [18] reported that AlSi40 functionally graded material can be produced by a one-step laser cladding process on cast Al-alloy substrates.…”

Phase formation and microstructure evolution in laser rapid forming of graded SS316L/Rene88DT alloy

“…In fact, a number of studies have been conducted on the laser rapid forming of functionally graded materials [10][11][12][13][14][15][16][17][18][19][20][21][22]; however, only a few studies concerning superalloys can be cited in the open literature [19][20][21][22]. Kahlen et al [19] employed the laser deposition of metal layers to create graded materials by varying the composition of the parts from 100% SS304 stainless steel to a 100% nickel-based superalloy.…”

“…He briefly studied the effects of the solidification rate on the mechanical properties of the graded materials. As for process development, Griffith et al [20,21] developed precise multiple-powder feeding capabilities for the laser engineered net shaping process (LENS TM ). The process has been used to fabricate graded or layered parts of stainless steel SS316/Inconel 690 and Ti6Al4V/Inconel 718 materials.…”

Solidification Behavior and the Evolution of Phase in Laser Rapid Forming of Graded Ti6Al4V-Rene88DT Alloy

“…[7][8][9][10][11][12][13][14][15][16][17][18] In the study of the capabilities of LRF for the fabrication of FGMs, Li [5] studied the influences of processing parameters on the forming characteristics of 316L stainless and nickel-base alloys. On the other hand, Griffith [10] and Lewis [11] developed precise multiple-powder feeding capabilities for the LENS and DLF processes, respectively. * These processes have been used to fabricate graded or layered material parts and have realized the preparation of SS316/In690, SS316/MM10, Ti/Ti20Nb, and Ti6Al4V/ In718 grade materials.…”