Powder catchment efficiency in laser cladding (directed energy deposition). An investigation into standard laser cladding and the ABA cladding technique

Abstract

This paper investigates the efficiency of powder catchment in blown powder laser cladding (a directed energy deposition technique). A comparison is made between standard “track by overlapping track” cladding (“AAA” cladding) and “ABA” cladding, where the gaps left between an initial set of widely spaced tracks (“A” tracks), are filled in by subsequent “B” tracks. In both these techniques, the melt pool surface is the collection area for the cladding powder, and the shape of this pool can be affected by several parameters including cladding speed, intertrack spacing, and type of cladding technique. The results presented here are derived from of an analysis of high-speed videos taken during processing and cross sections of the resultant clad tracks. The results show that the first track in AAA cladding has a different melt pool shape to subsequent tracks, and that the asymmetry of the subsequent track melt pools results in a reduction in the powder catchment efficiency. In contrast to this, the geometry of the “B” track melt pools between their adjacent “A” tracks results in an enhanced powder catchment efficiency.

Laser cladding: A high-speed-imaging examination of powder catchment efficiency as a function of the melt pool geometry and its position under the powder stream

“…On the left, the melt front substantially lags the powder stream in every case. Earlier work by the present authors 7 suggested that this is due to the laser interacting with the curved, sloping "shoulder" of the previous track, which means that the projected beam has a lower energy density (also, other factors such as angular dependence of absorption need to be taken into account).…”

“…From the software analysis of the HSI video, it was possible to identify the mass of incoming powder entering the melt pool as a percentage of the total powder feed rate, and this can be expressed as the powder catchment efficiency. 7 Figures for powder catchment efficiency can also be calculated by measuring the cross section of the clad tracks and, thus, the mass per unit time laid down in the clad layer. Both sets of results are presented in Fig.…”

“…Using techniques developed in earlier work, 7 the plan view geometry of the weld pool was accurately identified from the HSI videos. In each case, this could then be mapped onto the circular cross section of the vertically incident powder stream.…”

“…Three cladding techniques were compared: single track cladding ("A" cladding), standard, overlapping track cladding (AAA cladding), and a recently developed technique called ABA cladding. 6,7 These three techniques are described in Fig. 1.…”

Microstructure and Properties of Inconel 718 Coatings with Different Laser Powers on the Surface of 316L Stainless Steel Substrate

“…At present, there are many surface modification technologies, such as ion implantation technology [10], thermal spraying technology [11], and laser cladding technology [12]. Ion implantation technology requires high experimental conditions and needs to be carried out under high vacuum, which is not easy to operate.…”